Obesity and overweight have become increasingly prevalent in developing countries like China. This paper explores the evolvement of body mass index (BMI) of the Chinese population using a nationally representative sample. Focusing on familial transmission of BMI, we model married couple's BMI jointly and explore how parents' BMI affect children's BMI. In particular, we use spousal and parental characteristics as proxy variables to account for potential omitted variables bias and explicitly model common couple effect with the correlated random-effects model for couple' BMI. Our analysis suggests strong and positive spousal dependence and intergenerational transmissions of BMI in Chinese families. The influences of spousal BMI, parental BMI and a variety of social economic characteristics are found to depend on gender, region of residence (urban versus rural) and evolve over time. We find positive effects of spousal BMI that are significant, asymmetric (greater for wife than for husband), and generally vary across regions. For grown children, we find parental BMI to be the most important predictors for children's BMI. Since families can play an essential role in preventing obesity, our results can be useful for developing health intervention programs and promoting healthy lifestyle.