The purpose of this article is to explore the factors that are correlated with hours worked in China. A distinguishing feature of the study is that we used representative-matched employer and employee data. Hence, in addition to the usual worker characteristics examined in conventional economic models of labour supply, we also took into account the influence of firm characteristics and policies on the number of hours worked. The results suggested that in addition to the hourly wage rate, labour supply characteristics and human capital characteristics of the individual, firm-level differences are important in explaining variation in weekly hours worked in Chinese firms. In particular, our results suggested that there is a norm of longer working hours in firms that employ a high proportion of female and migrant workers, that hours worked are less in firms which pay overtime and that hours worked are less in firms in which labour disputes have disrupted production. The policy implications of Chinese firms reducing hours worked were discussed.