In China, there is a growing debate on the role of cultivated land conversion on food security. This paper examines the changes of the area of cultivated land and its potential agricultural productivity in China using satellite images. We find that between 1986 and 2000, China recorded a net increase of cultivated land (+1.9%), which almost offset the decrease in average potential productivity, or bioproductivity (-2.2%). Therefore, we conclude that conversion of cultivated land did not hurt China's national food security. We also show that more recent change in cultivated area also should have little adverse effect on food security.