The aim of the study was to investigate the relationship between the dietary concentrate-to-forage ratio and the chewing activity of the lactating dairy cows. Effects of dietary concentrate-to-forage ratio on the intake of nutrients (such as dry matter, neutral detergent fiber and physical effective neutral detergent fiber) and chewing activity (such as the eating activity and the ruminating activity) were evaluated using four primiparous Holstein cows with permanently ruminal cannula in a 4×4 Latin square design. Dietary concentrate-to-forage ratios were 30∶70, 30∶70, 50∶50 and 65∶35, respectively. The results showed that the dietary concentrate-to-forage ratio significantly (P<0.05 or P<0.01) affected the following: the intake of DM, NDF and peNDF; the feeding activities including daily feed time, single feed time, daily feed times and feed time per kg of nutrients (DM, NDF and peNDF) intake; the ruminating activities except single ruminating time and daily ruminating times of dairy cows; the chewing activities of daily chewing time, chewing time per kg of nutrients (DM, NDF, peNDF and ADF) intake and chewing times per kg of nutrients (DM and peNDF) intake of dairy cows. In conclusion, four diets with different concentrate-to-forage ratios could meet the requirements of peNDF and acquire the chewing time so as to maintain the appropriate milk fat percentage and rumen pH for the dairy cow by adjusting chewing activities.［Chinese Journal of Animal Nutrition, 2009，21(6):998-1005］