Although many studies have focused on how trustees’ particular or single social identity affects their trustworthiness, only one study has revealed that trustees with multiple social identities are judged as more trustworthy than those with a single identity. However, the study could not show how trustworthiness systematically changes with an increasing number of social identities. The present study addressed this issue and further explored in two experiments whether the growth trend of trustworthiness was particular to social identities. Experiment 1 showed that when the number of trustees’ social identities increased, they were judged as more trustworthy. Experiment 2 found that trustees with more social identities were judged as more trustworthy, whereas the amount of trustees’ personal physical information did not have that large effect in facilitating trustworthiness. These results demonstrate the special influence of social identity information on trust or trustworthiness.