A 3?3 duplicated Latin square experiment with 12 lactating Holstein cows (similar in body weight, calving period and milk yield, and days in milk was 50 to 120 d) was conducted to study the effects of different molasses supplementation on feed intake in 30 min and the whole day, and milk performance as well as the microbial protein production during the heat stress period in summer from July to September. Three kinds of molasses used in the experiment were blended molasses (BM), beet sugar molasses (SM) and yeast molasses (YM). A control group contained 12 cows was designed. The results showed as follows: feed intake in 30 min and daily feed intake were significantly affected by the supplementation of 3 kinds of molasses (P<0.01), in which those in BM group were the highest of all groups, followed by SM group, and BM group and SM group were significant higher than the control group (P<0.05); those in YM group were the lowest, and there were no significant differences in them between YM group and the control group (P>0.05). The milk yield in BM group and SM group was higher than that in YM group and the control group (P<0.05); somatic cell count and milk fat ratio in all groups were not significantly different (P>0.05). But somatic cell count in BM group and YM group had a tendency to decrease. BM supplementation significantly increased milk protein ratio compared with the other groups (P<0.05), but there were no significantly differences among SM group, YM group and the control group (P>0.05). Compared with the control group, adding 3 kinds of molasses significantly increased the production of the microbial protein of the dairy cows (P<0.05). In conclusion, the supplementation of BM in diets can alleviate the decrease of feed intake, and increase the milk yield and milk protein ratio of dairy cows during the heat stress period in summer.