The current study[4] was undertaken to evaluate the impact of P4C (Philosophy for Children) instruction using a community of inquiry method on students’ accountability. This quasi-experimental research had a pretest posttest control group design. The statistical population of the study included all female students of public high schools in Tehran in academic year 2015-2016. For the purpose of sampling, 50 students whose accountability was lower than average were chosen via multi-stage sampling method and were randomly assigned to experimental (N=25) and control (N=25) groups. The experimental group received P4C instruction using a community of inquiry method in 10 ninety-minute sessions, while the control group did not receive the intervention. In the posttest, both experimental and control groups were given the accountability questionnaire. In order to analyze the data, descriptive and inferential statistics (between group analysis of covariance) were utilized. Results showed that accountability of the students who had received P4C instruction was significantly higher than those who had not received such instruction. Thus, P4C instruction using a community of inquiry method is effective in promoting students’ accountability.