Using the Information–Motivation–Behavioral Skills (IMB) model as a theoretical framework, we examine the direct effects of knowledge, attitude, and subjective norms on young women’s intention toward purchasing green cosmetics, and whether self-efficacy mediates these effects. Data were collected from 433 young female consumers and analyzed using the PROCESS macro for SPSS. Green-cosmetics-related knowledge and motivation (attitude and subjective norms) were positively related to green cosmetics purchase intention. Self-efficacy partially mediated the effects of knowledge, attitude, and subjective norms on purchase intention. The IMB model offers a useful framework for understanding the factors affecting young Vietnamese women’s intention toward purchasing green cosmetics. Marketers promoting green cosmetics should aim to increase consumers’ confidence in comprehending their products.