Ground-level ozone is a continuing problem worldwide, but research about the influences of ozone pollution on labor productivity in developing countries is insufficient. Couriers are important for the rapidly developing express delivery industry and e-commerce around the world. Yet, they are susceptible to the health impacts of ozone pollution due to their typical outdoor working environments. We investigate the effect of ozone pollution on outdoor worker productivity in the service sector using a unique panel dataset of courier productivities from a top-five express delivery company in China. Using an instrumental variable constructed from ozone pollution of upwind nearby cities, we find that a 1-standard-deviation increase in daily ozone pollution decreases courier productivity by 6.84%. The same increase in ozone in the previous 30 days decreases worker productivity by 23.7%. Our findings emphasize an under-researched but important part of the socioeconomic costs of ozone pollution and call for policy attention on coordinated management of ozone pollution and particulate matters in developing countries.