A naturalistic method (concealed video camera) on the Library Plaza at Virginia Tech has been used successfully to document the climate-behavior relationships in outdoor space. Analysis of the data reveals that each climatic factor had certain types of relationships with outdoor human behaviors, and that it might be possible to predict the amount of outdoor activity occurring on the plaza under a specific climate profile. Due to the lack of previous research and data similar to our observations, we experienced some difficulties in comparing the results with previous research and in doing systematic analysis. The individual climate factors such as temperature, relative humidity, wind velocity, solar radiation, and the composite climate index, the Index of Thermal Stress, were analyzed to find a relationship with outdoor behavior. Graphic and statistical methods were used to analyze observation data. As the temperature on the plaza increased, there was a strong tendency for people to extend their time of stay on the plaza. But the temperature did not seem to have any strong relationship with the number or percentage of people who stayed on the plaza. Relative humidity appeared to have a negative correlation with the frequency of stationary behavior, but almost no relationship with average duration of stationary people. This finding conflicts with Givoni who reported that variations in relative humidity between 30% and 85% were almost imperceptible and at temperatures above 25°C, the influence of humidity on the response became gradually more apparent (Givoni,1981). Most of our observations were done under the temperature range of 0° ~ 25°C with a relative humidity of 30 ~ 85%. Under our observational condition (wind velocity less than 24 Km/hr), wind velocity had the strongest relationship with the frequency of stationary behavior. As the wind speed increased, the number and percentage of stationary people decreased almost linearly. Thus, wind velocity is a determining factor and the lower wind velocity is an impetus that induces people outdoors to pause or rest. The relationship between air velocity and the average duration of stationary people had a slightly negative correlation. The negative correlation was understandable, but, because it was negligibly weak, there was no meaningful relationship. Solar radiation did not appear to be an important factor for inducing people outside to stay on the plaza. But this study showed that the greater the solar radiation, the longer people stayed. The mean of the Index of Thermal Stress of Fall data was -139.268 and that of spring was 14.40. Therefore, in Fall, it was probable that people felt cold stress while in spring people were more likely to be comfortable. In Fall observations, the I.T.S. had a stronger relationship with frequency and duration of outdoor stationary behaviors than any single climatic factor. As the I.T.S. increased(in other words, as the cold stress decreased), more people stayed on the plaza and people tended to stay longer periods of time under the weather conditions in the fall of Southwestern Virginia. But, in spring observations, the relationships were much weaker than Fall observation. It was found that I.T.S. seemed to show a strong relationship between climate and outdoor behaviors if the I.T.S. values of data were completely negative or completely positive.