This paper investigates the effect of direct government control of land supply on the efficiency of China's urban land market. The authors find that: 1) Before 2004, residential land prices were positively and significantly related to property prices, indicating an efficient market where land prices reflected demand. 2) After 2004, when the government established direct control over land supply through auctions, the relationship between land and property prices weakened considerably. 3) This suggests that government control of land supply reduced market efficiency by weakening the influence of property demand on determining land prices.