This paper presents an experimental study to investigate the effect of inclination angle on the thermal performance of phase change material (PCM) based heat sinks without and with plate fins. Paraffin wax with melting temperature range 58–62 °C is used as PCM. Three different heat flux values such as 1.3, 2.0 and 2.7 kW/m2 are chosen to analyze the effect of heat flux variation on the melting of PCM. Also, tests are carried out with various angles of inclination from 0o to 90o at increments of 15o. The solid-liquid interface position is studied through photographic observation. Effect of angle of inclination and heat flux values on the operating and melting time has been reported. It has been observed that the operating time is relatively not dependent on the angle of inclination for the unfinned heat sink without PCM and three finned heat sink filled with PCM. The increase in operating time with the decrease in inclination angle from 90o to 0o is found to be 66%, 45% and 43% for PCM based unfinned, one finned and two finned heat sinks, respectively at set point temperature (SPT) = 75 °C and a heat flux of 2.0 kW/m2. Also, the melting time is found to decreases by 44% for unfinned heat sink and 30% for finned heat sinks with the reduction in inclination angle from 90o to 0o.