According to Poloma and Pendleton’s (1991) prayer model there are four prayer types (colloquial, meditative, petitionary, and ritual), all of which have varying associations with mental health. However, few studies have examined what mechanisms explain these associations. The literature demonstrates that disclosing distressing information can improve mental health. Thus, the current study examined self-disclosure as a mediating variable between Poloma and Pendleton’s (1991) prayer types and mental health. It was hypothesized that self-disclosure would mediate the association between prayer types involving meaningful communication with God (colloquial and meditative prayer types) and mental health and would not mediate associations between petitionary and ritual prayer types and mental health. This cross-sectional, online study analyzed data from praying Christian adults (N = 296) to test the hypotheses. As predicted, self-disclosure mediated the positive associations between colloquial and meditative prayer types and mental health. Self-disclosure was not associated with petitionary or ritual prayer and therefore did not mediate the relationships of these prayer types with mental health, as expected. Petitionary prayer had a negative relationship to mental health, while ritual prayer had a positive relationship to mental health. The results indicate that self-disclosure is an important mediator to consider when investigating the associations between private prayer and mental health.