Background: The assessment of the postmortem interval (PMI) represents one of the major challenges in forensic pathology. Because of their stability miRNAs, are anticipated to be helpful in forensic research. Objective: to see if estimation of PMI is possible using miRNA-122 expression levels in the heart samples from aluminum phosphide toxicity (Alpt). Methods: This was a cross sectional study on 60 post-mortem samples (heart tissues) collected at different intervals during forensic autopsies. The two groups were allocated equally according to the cause of death into Group I (control, n꓿30): Deaths caused by other than toxicity, and Group II (cases, n꓿30): Deaths due to Alpt. miRNA- 122 expression levels were measured in heart tissues at different PMI using RT-Q PCR.  Results: miRNA-122 level in Alp deaths was up regulated with statistically significant difference. There was positive correlation between miRNA-122 with PMI. Conclusion: The results of this study concluded that the PMI can be calculated using the degree to which particular miRNA-122.