Physical activity is recognized as a modifiable lifestyle risk factor that may prevent breast cancer. The aim of this cross-sectional study was to compare the physical activity patterns in two populations with different risks for breast cancer. We collected physical activity information from two groups of postmenopausal Canadian women with substantially different risks of developing breast cancer - Caucasians (N=372) and recent Chinese migrants from urban China (N=352). The frequency, duration, and intensity of occupational, household, and recreational activities were measured throughout the lifetime using the interviewer-administered Lifetime Total Physical Activity Questionnaire. Compared with Caucasians, Chinese migrants reported lower average total physical activity over their lifetime and for each age period (0-21, 21-29, 30-39, 40-49, and ≥ 50 years). Compared with Caucasians, Chinese migrants reported greater lifetime occupational activity, but lower levels of lifetime activity for both household and recreation activity. Among Chinese migrants, reported levels of occupational, household, and recreational activities were all greater in migrants from Mainland China than in migrants from Hong Kong. In conclusion, our results show that total activity was greater amongst Caucasians than Chinese migrants, suggesting that the lower breast cancer risk in urban Chinese women is not likely to be explained by greater total physical activity.