China's fifth population census taken on 1 November 2000 reveals that the mainland had a total population of 1,265.83 million, of which 455.94 million were urban residents (chengzhen renkou). This suggests that the level of urbanization was 36.09 per cent. Whereas this is a reasonable figure that appears to fit well the general rising trend of urbanization shown in the previous four censuses, the levels of urbanization reported in the five censuses are not really comparable because the criteria used to enumerate “urban” population have been different for different censuses. Before the State Statistical Bureau produces a set of comparable figures on the levels of China's urbanization based on a set of uniform criteria, the problem of data incomparability concerning the levels of urbanization will continue to baffle users. This report analyses the statistical criteria defining China's urban population used in the 2000 census, compares them with the criteria of the previous censuses and presents two sets of adjusted and internally coherent time-series data to remedy the problem of data incomparability.