Since 1958 the hukou (household registration) system has assigned Chinese citizens either a rural or urban status. Some studies argue that the rural-to-urban migrants in China who do not have urban hukou are not entitled to urban social insurance schemes, due to institutional discrimination, which applies differing treatment to urban and rural hukou (chengxiang fenge). Although rural-urban migrants participate less in the social insurance system than their counterparts with urban hukou, a closer examination of recent policy developments shows that migrants actually do have the legal right to access the system. This implies that discrimination between rural and urban workers has been declining, and distinctions based on household registration status are less able to explain China s current urban transition. This paper provides a new way of examining Chinese migrants social insurance participation, by adopting a framework that includes both rural-to-urban migrants and urban-to-urban migrants, which are an important, but less studied, migrant group. Among our key findings are that urban migrants are more likely to sign a labour contract than rural migrants; urban migrants have higher participation rates in social insurance than rural migrants; having a labour contract has a greater impact than hukou status in determining whether Beijing s floating population accesses social insurance; and urban migrants who have signed a labour contract have higher participation rates in social insurance than either rural migrants or urban migrants without a labour contract.