Nowadays, green roof is considered as a good strategy to improve the indoor hydrothermal environment. In order to investigate the influence of a light extensive green (LEG) roof on indoor temperature, humidity and human thermal comfort in summer in Chongqing, comparative experiments on two kinds of roofs, namely LEG and the common one, were carried out at two similar six-floor naturally ventilated residential buildings. The results showed that the room with LEG roof was characterized with a lower indoor temperature compared with the room with ordinary roof in summer. During the study period of July, monthly average indoor temperature of the tested room with LEG roof was 5.8℃ lower than outside and 4.9℃ lower than that of the room with ordinary roof at 14:00. On 24th July, the hottest sunny day in the study period, there was an obvious difference on indoor and outdoor temperatures of the room with LEG roof, which could reach as high as 7.6℃ at noon, while the indoor thermal environment had no significant temperature stratification. The humidity inside the room with LEG roof was relatively higher compared to that of the room with an ordinary roof. Assessed results from both PMV-PPD model and thermal sensation vote (TSV) indicate that LEG roof can significantly improve indoor thermal comfort. Higher level of indoor thermal comfort and lower indoor thermal dissatisfaction can be realized by the application of a LEG roof.