Aim: The aim of the research was to demonstrate the effect of genetic counseling on depression, anxiety and knowledge level among diabetes mellitus patients. Design: Quasi-experimental study. Methods: A quantitative study that used a questionnaire instrument to assess participants' levels of depression, anxiety, and knowledge. A total of 38 diabetes mellitus patients who met the inclusion criteria were studied for two months at the Lakbok Public Health Center with genetic counseling. Outcomes were measured before and after the counseling intervention provided. The statistical analysis was performed using the IBM SPSS version 25.0 software. Results: The results showed that the majority of participants (76.3%) had moderate depression prior to the genetic counseling intervention. However, after the intervention, most of the participants (73.7%) experienced mild depression, with a change in mean ± standard deviation (SD) pre-post 26.3 ± 3.1 to 17.6 ± 2.6. The anxiety level of most participants was moderate (73.7%). After the intervention, most participants experienced mild anxiety (86.8%) with a change in mean ± SD 16.7 ± 3.3 to 11.3 ± 2.3. In addition, before the intervention the knowledge level of the majority of the participants was satisfactory (86.8%). After the intervention, the knowledge level of the majority of the participants became good (52.6%) with a change in the mean ± SD of 12.8 ± 1.4 to 16.1 ± 2.3. Conclusions: Changes in the level of depression, anxiety and knowledge in different categories are real evidence of the consistency of the intervention's effect on these very significant factors that have implications for health services in various health facilities such as hospitals and public health centers. Therefore, serious efforts are needed so that health policies encourage the presence of genetic counseling services for DM patients and patients of other genetic diseases.