Single photon emission computed tomography (SPECT) is widely used for Nuclear Medicine. The low spatial resolution is mainly due to the limited collimator resolution. We have developed ordered subsets-expectation maximization (OS-EM) algorithm incorporating three dimensional spatial resolution correction (3D-SRC;horizontal and vertical direction) for distance-dependent blurring. In this paper we evaluate the fundamental properties of OS-EM algorithm including distance-dependent resolution correction using some phantoms (cubic phantom, cardiac and brain phantoms) and 12 patients performed 99mTc-tetrofosmin myocardial SPECT. In cubic phantom, the resolution in transaxial, coronal and sagital images are significantly improved by 3D-SRC. In short axial images of cardiac phantom, 3D-SRC shows more excellent images than no correction. In brain phantom, the blurring at the edge of the brain structure is improved by using OS-EM algorithm with 3D-SRC. In patients, the resolution in transaxial and short axial images is significant improved. These results suggest that this method improves the resolution in SPECT images and 3D-SRC is especially available in SPECT images of other axes in addition to transaxis. This method has advantage that both reconstruction and resolution correction are simultaneously performed. In the near future, we think that OS-EM algorithm incorporating attenuation, scatter and resolution correction will be used for quantitative SPECT images.