As volunteer engagement in non-governmental organizations vary between individuals, it is vital to get to know its predictors. It can be of profit to volunteers and the ones who profit from their activities. The aim of present study was to examine a model explaining volunteer engagement examining volunteer self-efficacy as a mediator and personality traits, job resources (skill variety and autonomy) as its predictors. Respondents (N = 165) were asked to fill in questionnaires accessible online. Those consisted of demographic questions as well as Ten-item Personality Inventory (TIPI), and three measures adjusted to volunteer environment: Work Design Questionnaire (WDQ), General Self-Efficacy Scale (GSES), and Work Engagement Scale (UWES). Results. Results of hierarchical regression analyses showed that conscientiousness, skill variety and self-efficacy are statistically significant predictors of volunteer engagement. It was shown that the effects of conscientiousness and skill variety on volunteer engagement are mediated by volunteer self-efficacy.