Background Shared decision making (SDM) is recognized as the gold standard for patient-centered care. This study aimed to assess and compare the SDM among patients undergoing hemodialysis and peritoneal dialysis for choosing a dialysis modality. Methods This is a cross-sectional study that was performed on 300 dialysis patients (218 HD and 82 PD) referred to two Dialysis Centers. Data were collected using demographic information and a 9-item Shared Decision Making Questionnaire (SDM-Q-9). The data were analyzed using ANOVA and independent t-test by SPSS software. Results The mean SDM-Q-9 score in all samples (PD and HD) was 21.94 ± 15.08 (in a possible range of 0 to 45). Results of the independent t-test showed that the mean SDM-Q-9 score in PD patients (33.11 ± 10.08) was higher than HD patients (17.14 ± 74.24) (p < 0.001). The results showed a statistically significant difference in mean SDM-Q-9 score based on patients’ age, educational level, and income (p < 0.05). Conclusion Implementing shared decision making and providing information on RRT should be started in the early stage of CKD. The health care providers should involve patients with CKD and their families in dialysis-related decisions and it should be started in the early stage of CKD.