Across four studies (N = 970), we investigated American men’s masculine gender nostalgia, or their sentimental longing for an ostensibly bygone era related to traditional masculinity when “men were men” and “women were women.” Prior work has found that group-based nostalgia uniquely predicts extreme forms of bias, including support for group-based violence. We investigated men’s masculine gender nostalgia and its effect on bias toward nontraditional women (i.e., working women, childless-by-choice women). In two correlational studies (Studies 1a and 1b), we found that masculine gender nostalgia was strongly associated with misogyny and acceptance of antitrans violence. Critically, masculine gender nostalgia was related to those outcomes above and beyond other measures of sexism (e.g., modern sexism, benevolent sexism) and relevant demographics (e.g., age, political conservatism). Study 2 experimentally manipulated male participants’ gender essentialist beliefs and found that increased gender essentialism predicted increased masculine gender nostalgia and, in turn, greater misogyny, bias against nontraditional women, and acceptance of violence against women. Finally, Study 3 manipulated male participants’ perceptions of the degree to which traditional masculinity has changed and become more feminine over time. Results indicated that American men who considered masculine decline reported increased masculine gender nostalgia, which in turn predicted greater bias toward nontraditional women, misogyny, and acceptance of violence against women. Discussion surrounds the importance of considering masculine gender nostalgia when investigating men’s bias toward women.