The purpose of this study is to investigate the factors that contribute to cognitive and affective trust of social robots. Also investi- gated were the changes within two different types of trust over time and variables that influence trust. Elements of trust extracted from literature were used to evaluate people’s trust of social robot in an experiment. As a result of a factor analysis, ten factors that construct trust were extracted. These factors were further analyzed in relations with both cog- nitive and affective trust. Factors such as Security, Teammate, and Per- formance were found to relate with cognitive trust, while factors such as Teammate, Performance, Autonomy, and Friendliness appeared to relate with affective trust. Furthermore, changes in cognitive and affective trust over the time phases of the interaction were investigated. Affective trust appeared to develop in the earlier phase, while cognitive trust appeared to develop over the whole period of the interaction. Conversation top- ics had influence on affective trust, while robot’s mistakes had influence on the cognitive trust. On the other hand, prior experiences with social robots did now show any significant relations with neither cognitive nor affective trust. Finally, Familiarity attitude appeared to relate with both cognitive and affective trust, while other sub-dimensions of robot atti- tudes such as Interest, Negative attitude, and Utility appeared to relate with affective trust.