Determination of age of bloodstain is a crucial subject in forensic field. This study was done to demonstrate the morphological changes occurring in white blood cells with time pass and correlate them with changes of pH level of the in vitro sample. Blood film stained with Hematoxylin and Eosin and pH level determination was done at times (0, 6, 12, 24, 48 and 60 hours) for in vitro blood samples left at room temperature. Lymphocytes were the most resistant cells for morphological changes with time; they appeared normal after 12 hours. Changes were detected after 24 hours in the form of pyknosis and degeneration of nucleus. Morphological changes of other types of white blood cells appeared after 12 hours in the form of pyknotic swollen nucleus, degenerated nucleus and cytoplasmic and nuclear vacuolation. After 60 hours, the nature and type of the cells (except lymphocytes) could not be identified. There was change in pH level corresponding with the morphological changes of white blood cells. The pH level was significantly decreased with pass of time. At 60 hours, pH level was (6.167±0.03) compared to its level (7.273±0.021) at zero time. It can be concluded that: The morphology of white blood cells and pH level of in vitro blood sample could give an indicator for the age of the blood