The concept of “migrant workers” derives from the household registration system of China’s planned economy period. The continued existence of that system conflicts with the development of an integrated labour market. The current social security system, based on household registration and a large number of local pools, discriminates against migrant workers because of their mobility and the lack of mechanisms to transfer benefits between pools. As a result, migrants have made major contributions to China’s economic development but do not get the same benefits as urban residents. Faced with this challenge, China’s government has begun to introduce policy reforms to improve social security for migrants. This article explores this development through a focus on old-age insurance. It analyses the special needs of migrants, the obstacles facing policy development and the proposed solutions. It argues that social justice and social equity require the development of a system that treats all citizens equally, and that the logic of an integrated labour market will ultimately require a unified national system of old-age insurance.