Background: Anxiety in orthopedic surgeries, especially knee replacement, is one of the most common complaints of the elderly. Aromatherapy with Damask Rose (Rosa damascena Mill.) can be one of the non-pharmacological methods in complementary medicine to control anxiety. Objectives: The present study aimed to determine the effect of aromatherapy with R. damascena on elderly anxiety after knee replacement surgery. Methods: In this quasi-experimental study, 80 elderly patients (60 to 90 years old) undergoing knee replacement surgery according to inclusion criteria were selected by convenience sampling method randomly from Moheb Mehr and Shafa Yahyaian hospitals of Tehran, Iran, and were divided into two groups of case and control. The case group was exposed to aromatherapy intervention at four intervals of 30 minutes. The instrument for measuring anxiety was the Visual Analogue scale for anxiety (VAS-A). Results: The results showed that the study elderly were homogeneous in terms of demographic variables in both case and control groups, except for two variables of education level and consumption of analgesics, which were also determined by two-way ANOVA. These parameters (education level, P = 0.54, and consumption of analgesics, P = 0.661) were not confounding variables. Significant differences were observed in the anxiety of the case group before and after the intervention (P < 0.001), while this difference was not significant in the control group (P = 0.304). Moreover, the difference in anxiety scores was significantly decreased after the intervention compared to before intervention in both case and control groups (P < 0.001). Probably Damask Rose aroma molecules produce and secrete neurotransmitters such as endorphins and encephalin, thereby reducing pain and anxiety. Conclusions: According to the findings of the study, the aromatherapy with R. damascena seems to be effective in reducing postoperative anxiety in these elderly patients.