Abstract A secular observer might assume that prayer practice affects those who pray by making the cognitive concepts about God more salient to their lives. Those who pray, however, often talk as if prayer practice – and in particular, kataphatic (imagination-based) prayer – changes something about their experience of their own minds. This study examined the effect of kataphatic prayer on mental imagery vividness, mental imagery use, visual attention and unusual sensory experience. Christians were randomly assigned to two groups: kataphatic prayer or Bible study. Both groups completed computerized mental imagery tasks and an interview before and after a one month period of practice. The results indicate that the prayer group experienced increased mental imagery vividness, increased use of mental imagery, increased attention to objects that were the focus of attention, and more unusual sensory experience, including unusual religious experience, although there were substantial individual differences. These findings suggest that prayer practice may be associated with changes in cognitive processing.