Background: Electronic portal imaging device(EPID)has different dosimetric characteristics than the ionization chamber, which is considered as the gold standard detector in radiation dosimetry. The main purpose of this study was to develop the applications of EPID. Dosimetric properties of amorphous silicon EPID (aS500) need to be investigated. Materials and methods: To verify linear response with dose, images of a 10×10 cm² open field were acquired. The EPID was positioned at a fixed detector distance of 150 cm, and varying doses were delivered with monitor unit settings of 1MU and 12MU. Results: The flatness should be less than 3%. The maximum flatness value was 2.7% for field size 10×10 cm² and 1.8% for field size 18×8 cm², which are within tolerance. EPID response was compared with the chamber dose. It was found that by increasing field size, both the EPID response and chamber dose were increased. The study showed that the EPID aSi500 has the potential to be used as a relative dosimeter, making it a very simple and efficient tool for daily QA. Conclusion: All EPID measurements were performed using the linear accelerator Varian DMX. The physical characteristics measured in this work suggest that the SLIC-EPID can be used be as a relative dosimeter.