Abstract: Objective To determine the level of moderate-to-vigorous physical activities (MVPA) and its relationship with gestational weight gains (GWG) in the second and the last trimesters of pregnancy. Methods A prospective study was conducted in Chengdu on 362 healthy pregnant women at the 24-28 gestation weeks who delivered a singleton. Demographic data and pre-pregnancy body mass were collected using a questionnaire. Weight gains at the gestation weeks of 24-28 and 32-36 were measured for the first two trimesters and the last trimester of pregnancy. The Denmark self-reported physical activity scale was used for measuring the duration and intensity of physical activities. Multiple linear regression models were established to determine the relationship between MVPA and GWG. Results The last trimester had lower average daily MVPA 〔（0.76±0.93) h〕 compared with the second trimester 〔（1.61±1.61） h, t=9.056, P<0.001〕. About 74.6% of the participants met the PA recommendations for the second trimester, compared with 60.5% for the last trimester (χ²=16.387, P<0.001). The participants experienced an average GWG of （7.36±3.78） kg during the first two trimesters, and （5.80±2.57） kg during the last trimester, corresponding to a growth rate of （0.30±0.15） kg/week for the first two trimesters and （0.51±CM(155mm 0.22） kg/week for the last trimester. Compared with the most inactive group, the participants with medium PAexperienced less GWG 〔（5.34±2.91） kg vs.（6.26±2.54） kg, P<0.05〕 and a lower GWG rate 〔（0.48±0.26） kg/week vs.（0.56±0.20） kg/week, P<0.05〕 during the last trimester. Age, gestational week, ethnicity, pre-pregnant BMI, GDM, pre-pregnant smoking and employment were associated with GWG and the GWG rates during the first two trimesters and the third trimester （P<0.05）. Compared with the most inactive group, low 〔-0.358（-0.691--0.026）〕 and medium 〔-0.762（-1.486- -0.037）〕 PA were associated with lower GWG during the last trimester. Moderate PA was associated with a lower GWG rate 〔-0.071（-0.133--0.008）〕 after adjustment for gestational age, energy intake, pre-pregnancy BMI and other potential confounders. Conclusion Insufficient physical activities are a serious problem in the pregnant women of Chengdu over the last two trimesters. Appropriate MVPA in the last trimester of pregnancy may reduce GWG and GWG rates.