Using China's 2005 1% population survey, this paper examines the wage impact on urban workers of rural to urban migration. We find that, on average, migrants increase the wages of urban workers, with the effect being magnified for more skilled urban workers. This suggests that migrants with skills similar to those of urban workers may complement them. We explore the possible channels of these effects. From the supply perspective, we find that migration inflows accelerate the occupational upgrading of urban workers, especially for low- and medium-skilled workers. From a demand perspective, as the share of migrants in the urban labor force increases, the number and output of industrial firms also increase, and firms become more reliant on low-skilled workers. The more migrants in a city, the greater the available employees for industrial firms, particularly for low-skilled employees. However, the effects on high-skilled firms are much smaller or insignificant. In addition, we find that migrants have little impact on firms' capital-labor and capital-output ratios. This suggests that firms can expand through capital adjustments to absorb inexpensive migrants, which alleviates the possible negative impact of migrants on the urban labor market.