This paper examines whether and how agricultural mechanization affects the BMI of farmers in rural China using a unique data set. We conducted a field experiment with face-to-face interviews in 135 counties of 12 provinces in China in 2013. It includes 4,229 individuals from 1,024 rural households, of which 1,033 of the 2,165 workers are farmers. The BMI of farmers who utilize agricultural mechanization is about 10 percent larger than those who don’t at a 1 percent significance level. Our results suggest that the adoption of agricultural mechanization has a positive and statistically significant effect on farmers’ BMI in China: it increases the BMI of farmers by 7.8 percent. Agricultural mechanization significantly reduces hours of farm work. The reduced hours of farm work due to the adoption of agricultural mechanization explain 30 percent of the BMI increase of rural farmers. Understanding BMI in rural China is important in order to define what public policies are most likely to be effective in preventing and reducing obesity in rural China.