The determining effect of personality similarity upon interpersonal attraction was investigated. (1) As for extraversion, 60 Ss assigned as extraverts or introverts rated 2 standard strangers, one extraverted and the other introverted on interpersonal judgment scales. They all were attracted the extraverted stranger as a whole. (2) As for need, complementarity as well as similarity hypothesis was examined. Another 80 Ss rated 2, nurturant and succorant strangers. Similarity effect was evident on nurturance, but not explicit on succorance. And complementary effect was only slightly found. Thus, the mediating factors underlying between personality similarity and attraction are reasoned. The functioning of the affective value of infomation is such.