Environmental migration has attracted much attention and is viewed as the avoidance behavior of populations faced with long-term exposure to air pollution. Using China's 2015 census data on migration, this paper estimates the impact of ambient air quality on labor migration between provinces. We find that one more polluted day (air quality index (AQI) > 150) at the original residence leads to a 0.6 percent increase in labor migration to a province with better air quality, providing evidence of the current migration trend leading to declining populations in China's megacities. This study suggests that if the environment can be improved, the local economy may benefit from attracting a skilled workforce from other provinces as well as from preventing the local population from migrating to other regions.