Gender inequality is one of the main barriers to human well-being. In societies with higher levels of gender inequality, people have lower levels of life satisfaction and happiness. However, previous studies have found inconsistent results in terms of whether gender inequality affects men’s and women’s subjective well-being differently. Furthermore, the psychological mechanisms by which gender inequality is associated with subjective well-being are still relatively underexplored. This study aimed to examine the following: (1) whether gender inequality would be associated with adults’ subjective well-being; (2) whether gender-role attitudes would mediate the effect of gender inequality on subjective well-being; and (3) whether the associations among gender inequality, gender-role attitudes, and subjective well-being would vary by gender. Drawing on data from 4,132 adults from 28 provinces in China (53.6% women; M = 50.95, SD = 16.92), multilevel analyses showed that adults in provinces with higher levels of gender inequality reported lower subjective well-being seven years later; moreover, this association was present not only among women, but also among men. Furthermore, multilevel mediation models indicated that less egalitarian gender-role attitudes accounted for the detrimental effects of gender inequality on subjective well-being. Our findings suggest the critical need to reduce socio-structural gender biases and stereotypical gender-role attitudes which hamper subjective well-being not only among women, but also among men.