Objective: To evaluate the effectiveness of nurse-administered Cognitive Behavioral Therapy (CBT) on reducing depressive symptoms among patients with Type II Diabetes Mellitus (DM) in Jordan. Methods: A quasi-experimental study was conducted with 100 patients diagnosed with Type II DM. Participants were divided into a control group (n=50) and an experimental group (n=50). The control group received usual care, while the experimental group underwent nurse-administered CBT sessions for a period of 1.5 months. Demographic variables included age, gender, socio-economic status, education level, and duration of Type II DM. The primary outcome measure was the severity of depressive symptoms, assessed using the Beck Depression Inventory (BDI). Pre-intervention and post-intervention BDI scores were compared between groups, and ANCOVA analysis was performed to control for demographic variables. Results: There were no significant differences between the control and experimental groups in demographic variables at baseline. In the experimental group, post-intervention BDI scores (M=20.5, SD=6.0) were significantly lower compared to pre-intervention scores (M=25.6, SD=8.4) with a mean difference of -5.1 (95% CI: -7.8 to -2.4, p<0.001). In contrast, the control group showed no significant changes in BDI scores between pre-intervention (M=24.9, SD=8.1) and post-intervention (M=24.1, SD=8.3) measurements, with a mean difference of -0.8 (95% CI: -3.4 to 1.8, p=0.838). Nurse-administered CBT had a statistically significant effect on the reduction of depressive symptoms after controlling for demographic variables, F(1,97)= 12.87, p= 0.001 according to ANCOVA analysis. Conclusion: This study concludes that Nurse-administered Cognitive Behavioral Therapy is effective in reducing patients with Type II Diabetes Mellitus's depressive symptoms. It is likely that including nurse-administered CBT into the standard diabetes care programs would improve these patients' mental health as well. More research is needed to evaluate the sustainability of the results and the possibility of applying such approaches in other conditions.". Keywords: Nurse-led CBT, Type II Diabetes Mellitus, Depression, Depressive Symptoms, Beck Depression Inventory, Quasi-experimental study.