China's new Labour Contract Law took effect in January 2008 and required firms to give migrant workers written contracts, strengthened labour protections for workers and contained penalties for firms that did not follow the labour code. This article uses survey data of migrant workers in the Pearl River Delta before and after the law, and a retrospective question on when workers received their first labour contract to assess the effects of the law on labour outcomes. The evidence shows that the new law increased the percentage of migrant workers with written contracts, which in turn raised social insurance coverage, reduced the likelihood of wage arrears and raised the likelihood that workers had a union at their workplace.