Background: Type II diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and impaired glucose metabolism. This study aimed to investigate the decline in estimated glomerular filtration rate (eGFR) and its association with mortality in patients with type II diabetes mellitus (T2DM) over a 12-month period. It also sought to identify potential factors contributing to eGFR decline and mortality in this cohort.Materials and Methods: A prospective cohort study was conducted at a tertiary care hospital with 105 patients diagnosed with T2DM. Participants were enrolled from the outpatient diabetes clinic, and inclusion criteria were adults aged 18 years or older, a diagnosis of T2DM for at least 2 years, and baseline eGFR data available within 6 months prior to enrollment. Participants were followed up for 12 months with clinical visits every 3 months. Renal function was monitored by measuring serum creatinine levels and calculating eGFR using the CKD-EPI formula. Mortality events and causes of death were also recorded. Descriptive statistics, univariate and multivariate analysis, and survival analysis methods were employed for data analysis.Results: Over the 12-month follow-up period, a significant decline in eGFR was observed, with the mean eGFR decreasing from 78.6 ± 12.5 mL/min/1.73m² at baseline to 71.4 ± 12.4 mL/min/1.73m² at 12 months. Factors such as older age and longer duration of diabetes were significantly associated with a greater decline in eGFR. Among the 12 deaths recorded during the study, the most common causes were cardiovascular disease (41.7%), kidney failure (33.3%), stroke (16.7%), and infection (8.3%). Multivariate regression analysis identified age and diabetes duration as independent predictors of significant eGFR decline.Conclusion: This study confirms that eGFR declines significantly in patients with T2DM over a 12-month period, with age and longer diabetes duration as key predictors. The high mortality rate, particularly due to cardiovascular disease and kidney failure, highlights the need for early monitoring and intervention to prevent renal deterioration and reduce mortality risk in this population.