Two processes intermediating conversation in social interaction of dyadic relationship were examined. In the first process, some antecedent factors such as task situation, interpersonal relationship and personal difference influence on conversation process. In the second process, the conversation influence on some interaction of the dyadic relationship. In our experiment, we set a topic of conversation into a decision making in problem-solving conversation as the task situation. And a degree of intimacy (high or low) as interpersonal factor and combinations of self-monitoring tendency (high-high high-low low-low) as personal factor were manipulated. 112 undergraduates were administrated self-monitoring scale. And 61 dyads were made of them and were measured their degrees of intimacy. After that, they are engaged in conversation about a given topic that is asked to make a decision. And then, they were asked to answer a questionnaire that survey social interaction. The results were as follows; (1) The total numbers of protocols in the conversation were influenced by intimacy. (2) The numbers of protocols which represent the qualitative differences of the conversation were influenced by intimacy and by combinations of self-monitoring tendency. (3) The qualitative differences of the conversation influenced on the cognitions and the evaluations to the conversation process and the partner.