This case study compares the environmental efficiency of non-certified organic and conventional rice production in southern China. Using plot-season level survey data, we test the existence of a "technology gap" between the two types of production, and calculate their environmental efficiency scores based on the level of pure nitrogen use, which is considered as an environmentally detrimental input within the framework of the stochastic frontier analysis. Our analysis reveals that organic farming loses its environmental performance at high nitrogen levels and that during the initial conversion period to organic farming newly converted organic farmers increase the use of external nutrients such as nitrogen to compensate for potential yield losses. These results highlight the uncertainty with which conventional farmers initially tend to view organic farming. However, we find that the experience gained by organic farmers over time helps them increase and maintain the environmental efficiency. Wewarn against the rapid expansion of organic farming and recommend more technical support and strict nutrient regulation to foster the environmental efficiency of organic farming.