The adverse effects of antibiotics on ecological health of aquatic environments is increasingly a social and scientific concern. Here we investigated the occurrence, distribution, and risk assessment of residual antibiotics in the main drinking water source (Baitiao River and Xuyan River) of Chengdu, China. Five commonly used antibiotics including sulfamethoxazole, tetracycline, roxithromycin, erythromycin, and chloramphenicol were tested in the two rivers with concentration ranging from less than limits of quantification to 3.62 ng L^-1. Among them, tetracycline was persistent in surface water and exhibited no significant differences along the flow direction of the two rivers. Compared to other rivers or surface waters in the world, the concentrations of the five antibiotics in present rivers were mainly below average levels. All the risk quotients of detected antibiotics in the rivers were lower than 0.001, suggesting that they were at a low level of ecological risk across trophic levels of aquatic organisms.