Since the late 1980s, massive rural - urban migration in China has attracted considerable attention from economists and policymakers, both within and outside China. One of the most striking features of rural - urban migration is that job attainment among the migrants differs considerably between males and females. It is of great interest to know the reasons for this difference and, more importantly, whether gender occupational segregation has a large impact on the gender wage differential among migrants. This paper examines these issues using data on 1504 migrants collected in Jinan city, Shandong province. It is found that gender occupational segregation in this sector is mainly due to the unequal treatment of male and female attributes in occupational assignment and that this contributes very significantly to the gender wage differential among migrants. A comparison with another study on China's rural industrial labour market is made, which suggest that intra-occupational gender wage discrimination is lower in the labour market for rural - urban migrants than in the labour market in the rural industrial sector.