Quality assurance (QA) of clinical treatment machines is necessary for any radio therapy center. The purpose of QA clinical machines is to measure actual performance and compare with the existing standards, or reference value. QA procedures are designed to minimize i.The difference between prescribed and delivered dose, ii.The time between occurrence of error and implementation of corrective action, and to prevent the delivery of unintended dose. In this regard the dosimetric characteristics of Siemens Primus Plus linear accelerator (LA-1) and Primus linear accelerator (LA-2) were analyzed in this study. LA-1 has photon beams of nominal energy 6-MV and 15-MV and electron beams of 6, 9, 12, 15, 18 and 21-MeV. Similarly LA-2 has photon beams of nominal energy 6-MV and 10-MV and electron beams of 5, 7, 8, 10, 12 and 14-MeV. In this study the similarity in photon dosimetry data was investigated for nominal photon energy of 6-MV of both linear accelerators at KIRAN.