Creating a favorable thermal environment in an outdoor space is essential for attracting more occupants to outdoor areas and vitalizing a city. It is possible to study occupants' needs in an outdoor thermal environment by observing their attendance and behaviors, since people may exhibit certain adaptive measures, such as seeking shade, using parasols, etc., "vote with their feet", or even leave the space, if they feel uncomfortable. In order to investigate the influence of thermal environment on attendance and adaptive behaviors in outdoor spaces, in this study we carried out field campaigns in a university campus in a cold-climate city. The thermal environment was monitored, while surveys of thermal perceptions and observations of attendance and adaptive behaviors were conducted. Through the data analyses, it was found that the thermal environment had a great impact on the attendance of optional activities, but necessary activities were not influenced. The greatest influence on attendance came from air temperature. The influences of wind and humidity on attendance were found to be coupled with that of air temperature. Adaptive behaviors, such as seeking shade, using parasols, changing clothes, and changing the lengths of stay, were also greatly influenced by air temperature.