We propose a subjective quality estimation model for interactive multimodal services. First, psychological factors of an audiovisual communication service are extracted by using the semantic differential (SD) technique and factor analysis. Forty subjects participate in subjective tests and perform point-to-point conversational tasks on a PC-based TV phone that exhibits various network qualities. Those subjects assess those qualities on the basis of 25 pairs of adjectives. Two psychological factors, i.e., an aesthetic feeling and a feeling of activity, are extracted from the results. Moreover, overall audiovisual quality can be estimated by evaluating scores of the above two psychological factors. Second, quality impairment factors affecting these two psychological factors are analyzed. We find that the aesthetic feeling is mainly affected by IP packet loss and video coding bit rate, and the feeling of activity depends on delay time and video frame rate. We then propose an opinion model derived from the relationships among quality impairment factors, psychological factors, and overall quality. Our calculations indicate that the estimation error of the proposed model is almost equivalent to the statistical reliability of the subjective score. Finally, using the proposed model, we discuss guidelines for quality design of interactive audiovisual communication services.