In urban planning it has become more important to consider climatic comfort in the outdoor open spaces such as parks, streets, etc., to make up higher-grade residential environment. However, relation between human thermal sensations and surrounding climatic conditions or thermal indices is not yet made so clear in the outdoor environment as in the indoor ones. Thus the experiments on human thermal sensation were conducted in the shade of trees and in sunshine during summer season. This paper mainly describes Comfort sensation in relation to other thermal sensations and thermal indices. Temperature sensation is most highly correlated with Comfort sensation and Sweatiness and Radiation sensations are next to this. Wetness sensation has low relation with Comfort as a whole. Air Flow sensation is moderately related in treeshade but low in sunshine. ASHRAE's Standard New Effective Temperature, SET*, is recommended as a fairly good thermal index for out-door environment, having high correlation with Comfort sensation in comparison with Discomfort Index and Wet-Bulb Globe Temperature Index. SET* from 27℃ to 28℃ is considered to be the threshold for comfort in the out-door environment, based on the cumulative frequency distribution of SET* for each category of Comfort sensation. Comfortable temperature, T_<a・cal>, calculated by Penwarden's comfort equation is inclined to be less than measured value, T_<a・meas・> R_b, thermal resistance of body tissue, equal to 0.04 m^2℃/W (onset of sweating) gives better agreement between T_<a・cal> and T_<a・meas・> rather than R_b equal to 0.065 m^2℃/W (no sweating, i.e., most comfortable) does. The better T_<a・cal> agrees with T_<a・meas・>, the higher wind speed, the higher comfortable level of Comfort sensation and the lower Sweatiness sensation.