The main purpose of this study was to examine how the existence of multiple Prisoner's Dilemma relations among group members affects their choices in each PD relation. Twenty-eight computer simulated actors were used to simulate group members. Each simulated-actor had two kinds of strategies: (1) designation strategy (i.e., strategy to determine whom to choose as a game partner), and (2) behavior strategy (i.e., strategy to determine when to cooperate and when to defect). The simulation involved four designation strategies, and seven behavior strategies. Five of behavior strategies were variants of the tit-for tat strategy, said to be most effective in iterated 2-person PD games. Results of the simulation indicate that: (1) the designation strategy has a greater influence on the simulated-actor' total score than the behavior strategy; (2) effectiveness of the behavior strategy changes depending on the designation strategy adopted; (3) the relationship between disignation and behavior strategies mentioned above depends on the nature of the pay-off matrix used in each game played along the PD network.