Introduction: Estimation of time since death remains an important issue in forensic investigations and the eye has a great value in this field. Objective: This work was designed to prove the Correlation of both potassium level in vitreous humor and histopathological changes in rat's cornea to time since death. Material and Methods: Sixty adult male albino rats were divided equally into 2 main groups. Group 1 was subdivided into six groups according to known postmortem intervals (0, 24, 48, 72, 96 & 120 hrs). It was used for chemical estimation of potassium level in vitreous humor at each time interval. Only the clear samples of vitreous humor were taken after exclusion of any injured or diseased eye. Group 2 was subdivided into six groups at the same postmortem intervals and used for detection of histopathological changes in rat's cornea by both light microscope (Toluidine blue stain) and scanning electron microscope (SEM). Results: As regard biochemical results, vitreous humor samples showed significant time dependent increase in the potassium level up to 120 hours postmortem. Regarding histopathological results, light microscopical examination of rat's cornea showed gradual degenerative changes from 24 hrs postmortem in the form of cloudy swelling and separation between its layers to complete necrosis of epithelial cells (only clusters of basal cells seen attached to cell membrane) at 96 hrs postmortem, while the endothelium showed slight affection at 24 hours postmortem, then subjected to gradual degenerative changes to complete necrosis and loss of its cells at 72 hours postmortem, finally, the details of the cornea were not obvious in both epithelium and endothelium at 96 hours postmortem. Scanning electron microscope (SEM), confirmed the previous results in the epithelial layers with gradual desquamation, while the endothelium is nearly normal at 24 hrs postmortem. Then, gradually increased to show loss of the endothelial cells at 72 hrs postmortem with final loss of cyto-architecture pattern in both epithelium and endothelium up to 120 hrs postmortem. Conclusion: potassium level in vitreous humor shows gradual time dependent increase in its level up to 120 hours. The changes in the rat's cornea are considered as good indicator of postmortem interval up to 96 hours using light and electron microscope, so, we can depend on one of these method or both of them not only for crime investigation to estimate time since death, but also in corneal donors for corneal transplantation.