Background: Organ donation is one of the main medical advances in treating patients with organ failure. However, the supply of transplant members is much below such patients’ demands, thereby arousing a serious challenge to governments. Organ donation is a sacrificial and altruistic behavior, and altruism is recognized as an effective factor in making decisions for organ donation. Objectives: This study aimed to investigate the relationship between altruism and attitudes toward organ donation in society. Methods: The present research was a cross-sectional descriptive study conducted in Iran during 2020 - 2021. The research sample encompassed328 individuals selected using the simple random sampling method. Data collection tools included a demographic information form, the standard Self-Report Altruism Scale, and the Attitude Toward Organ Donation Questionnaire. Linear regression controlling the intervening variables was used to investigate the relationship between altruism and attitudes toward organ donation. Results: The univariate analysis results showed that gender, occupation, age, and marital status were not significantly correlated with attitudes toward organ donation. In the multivariate model controlling the intervening variables, altruism increased attitudes toward organ donation (beta-standardized = 0.17; P < 0.001). Conclusions: The findings highlighted the significance of altruism in attitudes toward organ donation. Accordingly, intervention programs promoting altruism can be helpful in different groups.