Our paper introduces the dimension of social psychology in a model of efficiency wages and gender diversity. In this context, we show that women earn lower wages than men but provide in return relatively less effort. Therefore in order to increase women’s productivity, the firm increases their level of employment. In our efficiency-wage theory, women’s lower wages is explained by assuming that efficiency-wages function for women are believed to be different from those of men. This could be the case if the firm believes that women do not react with more effort to higher wages because they are not work career oriented, so it might not be worth it to pay them high wages. In that case, firms would employ more women for the minimum possible wage. This assumption can be based on stereotypes describing about women as more averse to wage competition pressure than men and less career oriented.