Warmth (including friendliness, trustworthiness, well-being, and morality) and competence (related to goal attainment, including competence, ambition, intelligence, efficiency) are the two fundamental dimensions (i.e. Big Two) in social cognition. Previous research explored the relationship between warmth and competence and found that warmth judgments were primary. However, there are certain boundary conditions for the primacy of warmth. Previous research indicated that interdependence might have moderate effect on the primacy of warmth, but the conditions under which interdependence leads to a reversal of the primacy of warmth to the primacy of competence have not been clearly answered. The current study proposes the “interest-interdependence hypothesis”, which states that in an interest interdependent relationship, the primacy of warmth is reversed to the primacy of competence. This study intends to compare preferences for warmth and competence in short-term cooperation with strangers and test the “interest-interdependence hypothesis” by comparing cooperation and neutral scenarios. Study 1a explored preferences for warmth and competence in cooperation from the perspective of others and tested the “interest-interdependence hypothesis”. Fifty university students were assigned to 2 (scenario: cooperation scenario vs. neutral scenario) × 2 (dimension: warmth vs. competence) mixed design. Half of the participants in the cooperation group read the cooperation scenario materials and others in the neutral group read the neutral scenario material. Then all the participants received a list of 16 traits (8 on warmth dimension, 8 on competence dimension) and were asked to choose 8 of them. The results of Study 1a showed that more warmth trait words (as compared to words on the competence dimension) were chosen in neutral group and more competence words (as compared to words on the warmth dimension) were chosen in cooperation group. Study 1b used the warmth and competence trait importance rating task to replicate preferences for warmth and competence in cooperation when perceiving others. Seventy participants were recruited and assigned to mixed design (same as study 1a). Participants in both groups read the corresponding scenario material separately (as in study 1a), and then they were asked to rate the importance of 30 traits (15 on warmth dimension, 15 on competence dimension) in evaluating others in the scenarios they just read. The results showed that, participants in neutral group scored significantly higher on warmth than competence. In contrast, participants in the cooperation group scored significantly higher on competence than warmth. Taken together, findings from these two studies provided evidence to support our “interest-interdependence hypothesis” from the perspective of others. Study 2 explored preferences for warmth and competence in cooperation from the perspective of self. Seventy-six university students were randomly assigned to cooperation group and neutral group, and then read the corresponding scenario material separately (same as in study 1a and 1b). Then they were asked to rate the importance of 30 traits (same as study 1b) in evaluating themselves. The results showed that competence traits were rated as more important than warmth traits in both groups, but the primacy of competence was more pronounced in the cooperation group. The present study not only answers, for the first time, the question of which is more important in cooperation, warmth or competence, but also clarifies the the conditions for the reversal of the primacy of warmth to the primacy of competence in the interdependence and provides initial evidence for the “interest-interdependence hypothesis”.