Radiation dose reduction and improved image quality in nuclear medicine scan is most important factor in nuclear medicine imaging. In this paper, we simulated kidney scintigraphy to examine the effect of the amount of the injected radiopharmaceutical, energy window, and type of collimator on the image quality of renal SPECT. We used SIMIND software to simulate SPECT system equipped with LEHR and LEGP collimators. The images of kidneys were obtained by use of the NCAT phantom with activities of 2mCi(75 MBq), 5mCi (185MBq) and 10mCi (370MBq) by use of the energy windows of 10 and 20%. Then, the images were compared with the reference image by MATLAB software. Assessment of comparison between results show that the best result could be obtained by use of the narrow window width energy and injection of the high activity. By use of the LEHR collimator, energy window of 20% could be produced images with higher quality in lower administered activity, while in high activity, the best result could be obtained by use of the window width of 10%. The window width of 10% responds better in LEGP collimator and this collimator works well in higher activities with lower window width energy.