Cardiovascular diseases (CVDs) are the most common cause of morbidity and mortality globally. This is due to the increasing prevalence of modifiable CVDs risk factors such as high blood glucose, high systolic blood pressure, high low-density lipoprotein cholesterol and obesity. Certain evidence also indicates that increased burden and severity of CVD due to the additive and synergistic effect of the presence of multiple modifiable CVD risk factors. However, there is a scarcity of information about knowledge of modifiable risk factors for CVD among Type-II diabetic patients attending public hospitals at Shashemene, Oromia Region, Ethiopia. Therefore, this study was designed with major objectives to assess the diabetic patients' knowledge about modifiable cardiovascular disease and primary prevention practices, and to identify risk factors in Shashemene public hospital, West Arsi zone, Oromia, Southern Ethiopia, in 2023. To this end, an institution-based cross-sectional study was conducted among diabetes mellitus patients on follow-up at public hospitals in Shashemene Town in March 2023. The collected data was checked for completeness, coded and compiled. The data were entered into SPSS version 20 for further analysis. Both descriptive and analytical results were used to present the findings. In this study 418 type II diabetes patients were participated. Of these, 64.6% were male and the mean age of study participants was 44 ± 15 year. The diabetic clients who had good knowledge of modifiable CVD risk factors were 51.4% and also about 41.4% showed good practices. Moreover, the patients attained primary school had more than 2 times knowledge of CVD risk factors than illiterate ones [AOR: 2.78 (1.64,4.71)p-0.01. Similarly, females had 39% less knowledge and about the modifiable risk factors compared to men [AOR: 0.61 (0.40, 0.92)P-0.01]. Singles were more than 2 times knowledgeable about modifiable risk factors [AOR: 2.42(1.33, 4.40) p-0.00]. Furthermore, college educated patients were more likely to be aware of modifiable CVD risk factors [(AOR: 2.13(1.05, 4.34), p0.03)] than others. In the same way, merchants had more knowledge and showed better primary prevention practices of modifiable CVD than farmers [AOR: 2.33(1.11, 4.89), p-0.01]. In conclusion, the proportion of diabetic patients having good knowledge of modifiable cardiovascular disease and good primary prevention practices were 51.4% and 41.4%, respectively in Shashemene. Besides, illiteracy, sex, marital status, education level and occupation were identified as risk factors for knowledge about modifiable CVD and primary prevention practices. These results may provide some hints for programs targeting fighting against CVD among type-II diabetic patients in Oromia Region.