Based on survey data from seller firms, we investigate the effect of trust and commitment on sellers' relational behavior and its performance implications. Empirical results indicate that both trust and commitment positively influence seller cooperation and flexibility in business relationships,but the effect of commitment is larger than that of trust. The results also show that sellers'opportunistic behavior is less when their affective commitment is high. Another important finding is neither trust nor commitment predicts sellers'formal control mechanism usage.And last, we find out that sellers'cooperation and flexibility have significant positive influence on relational performance.