Postmortem Interval (PMI) is determined by biochemical composition of body fluids. The present work aimed for assessing the postmortem electrolytes (potassium, sodium, chloride, calcium) as well as urea concentrations in both blood an vitreous humor in 50 medicolegal autopsy cases, The following results were obtained:1.There was no significant difference in all parameters levels between the two eyes, and between both sexes as well as between the levels of sodium, chloride, calcium and urea with the postmortem interval.2.There was a significant correlation between the potassium level in both blood and vitreous humor with the postmortem interval.3.A proposed formula for calculating postmortem interval was obtained in the present study and was: PMI = 3.5086 + 1.9338 x Mean vitreous [K+]4.In order to increase the precision of the regression equation, we exclude cases of vitreous urea more than 100 mg/dl (6 cases), and the proposed formula to calculate PMI is: PMI = 1.406 + 0.419 x Mean vitreous [K+]5.The estimation of PMI using the equation of the present study is of better accuracy than the estimates that use the previously published ones.6.It was evident that using both potassium and calcium measurements to estimate the PMI were associated with increased accuracy than using potassium alone: PMI = 2.14 x Vitreous [K+] + 0.104 x Serum [K+] + 0.412 x Serum [Ca++] – 0.784 x Vitreous [Ca++] -1.46The present study recommends further work using a larger number of cases and for a longer postmortem period of time and the correlation between blood and vitreous electrolytes levels with the postmortem interval. Also, the effect of various environmental factors and different modes of death on the accuracy of the proposed equations needs further studies.