In outpatient clinics, appointment systems usually consider the rules that focus on patient arrivals such as single block or multi-block. In an individual block, a patient arrives at the beginning of the session, while in multi-block, more than one patient arrives at each scheduled appointment interval. However, these scheduling rules don't take into account the utilization of resources (i.e., doctor's service) that is another factor for appointment systems. In this study, we investigate two important factors imposed to the appointment system of outpatient clinics simultaneously using a simulation technique. Appointment scheduling rule (ASR) focuses patient arrival in clinics and selection rule (SR) focuses on patient assignment to multiple severs (doctors). The built simulation model takes into account a multi-facility system in which two consultation rooms are considered. The first consultation room is affected by the two factors of SR and ASR. Subsequently, the second consultation room is only affected by the factor of ASR since patients need to return to the same doctor in the first consultation room. To evaluate the performance of the simulated appointment system, we employ two standard measures such as patient waiting time and doctor idle time. The objective is to achieve that both the waiting time and the doctor idle time in an outpatient clinic system are minimized. The experimental results show better efficiency by considering both the ASR and SR simultaneously, compared to the conventional approach only considering the ASR.