Abstract: The measurements of scatter factor are carried out using diode and RK ionization chamber for 6 and 15 MV medical linear accelerator energy photons in water phantom. The photon energy spectra for 6 and 15 MV in water phantom are also calculated using Monte-Carlo method. The aim of this paper is to correct the error resulting in the overdosing of diode detector due to low energy scatter photons. The paper also supports the quality assurance(QA)and quality control(QC) in radiotherapy physics.