Background: This research was conducted to investigate the effects of a nursing supportive program on anxiety and stress levels in the family members of patients admitted to the intensivee care unit (ICU) after cardiac surgery. Methods: This research was a quasi-experimental study. A control group and an intervention group (each = 35), both comprised of the family members of post-cardiac surgery patients admitted to the ICU, were studied. The intervention group received a nursing supportive program initially 2 hours after their patients entered the ICU (1st day) and thereafter on the 2nd and 3rd days. The control group received only the routine information. Demographic variables and an adjusted Depression Anxiety Stress Scales (DASS-21) were used to assess the anxiety and stress levels of the family members of the patients. Results: Demographic variables and the DASS scores had no statistically significant differences in stress levels between the 2 groups before the intervention. However, after the intervention, the mean score of the stress level in the intervention group dropped significantly in comparison with the control group (P = 0.0001). Anxiety levels in both groups were reduced after the intervention. However, although a statistically significant difference was observed between the 2 groups 2 hours after ICU admission and on the 2nd ICU day (P = 0.0001), there was no significant difference on the 3rd ICU day (P = 0.993). Conclusions: In light of the findings of the present study, our nursing supportive program, which was aimed at providing information, emotional and mental support, and reassurances to the family members of post-cardiac surgery patients hospitalized in the ICU, was able to decrease their stress levels and to some extent their anxiety levels.