The effects of different protein sources [corn gluten meal, soybean meal, poultry meal 65 (low protein content, 65%), poultry meal 80 (high protein content, 65%), fish meal, and duck frame meal] diets on feed intake, nutrient apparent digestibility and fecal quality of Tibetan mastiffs during different growth stages were evaluated in this study. Ten puppies (5 to 6 months old) and ten adult canines (2 or more years old) were selected and randomly divided into 2 groups, respectively. Each group contained 5 replicates and each replicate contained 1 canine. Seven experimental diets were formulated as follows: CGM (only corn gluten meal as the plant protein), SBM (only soybean meal as the plant protein), PMH-FM (both poultry meal 80 and fish meal as the plant protein), PML-FM (both poultry meal 65 and fish meal as the plant protein), DM-FM (both duck frame meal and fish meal as the animal protein), FM (only fish meal as the animal protein) and PML diets (only poultry meal 65 as the animal protein), respectively. Each diet fed one group of young and adult Tibetan mastiffs, respectively. The experiment was divided into 4 periods, and each period lasted for 10 days with 6 days for adaptation and 4 days for the collection of fecal samples. The results showed as follows: for the diets with different protein sources, the average daily feed intake of puppies was not significantly different (P>0.05). The average daily feed intake of adult canines for PML-FM diet was no significant difference compared with PMH-FM diet (P>0.05), but was significantly higher than that for other diets (P<0.05). Under the condition of feeding the same diet, the average daily feed intake of puppies was significantly higher than that of adult canines (P<0.05). For puppies, the dry matter (DM), crude protein (CP), organic matter (OM), calcium (Ca) and total phosphorus (TP) apparent digestibility of PMH-FM diet was the highest, all above nutrient apparent digestibility was significantly higher than that of PML-FM diet (P<0.05), CP apparent digestibility was also significantly higher than that of PML diet (P<0.05), and TP apparent digestibility was also significantly higher than that of DM-FM and FM diets (P<0.05). For adult canines, the DM apparent digestibility of SBM diet was significantly higher than that of PML-FM diet (P<0.05), and the CP apparent digestibility of DM-FM diet was significantly higher than that of PML and PML-FM diets (P<0.05), while the TP apparent digestibility of FM diet was significantly lower than that of SBM and PML-FM diets (P<0.05). There was no significant difference in OM and Ca apparent digestibility for adult canines among all diets (P>0.05). Under the condition of feeding the same diet, the DM, CP and OM apparent digestibility was not significantly different between puppies and adult canines (P>0.05); however, the Ca and TP apparent digestibility for puppies was significantly higher than that for adult canines when fed the PMH-FM diet (P<0.05). When fed the PMH-FM diet, the puppies had the lowest fecal original moisture content, which was significantly lower than that of other diets except PML-FM and DM-FM diets (P<0.05). When fed the FM diet, the adult canines had the highest fecal original moisture content, which was significantly higher than that of other diets (P<0.05). The fecal scores of puppies fed CGM, PMH-FM, PML-FM, DM-FM and FM diets were all about 2.5 (optimal fecal score), while the fecal scores of puppies fed SBM and PML diets were about 2.8. The fecal scores of adult canines fed different diets had no significant difference (P>0.05). Under the condition of feeding the same diet, the fecal original moisture content was not significantly different between puppies and adult canines (P>0.05), but the fecal score of puppies was significantly higher than that of adult canines (P<0.05). It is concluded that diets with different protein sources have some influences on the nutrient apparent digestibility and fecal quality of Tibetan mastiffs, and have greater influences on the puppies. Combined use of the corn gluten meal and soybean meal is better than signal use of them, and the poultry meal 80 with high protein content is a better protein source compared with the fish meal and poultry meal 65 with low protein content for Tibetan mastiffs.