Background. In the field of positive psychology, mindfulness and character strengths have gained much attention in research because of individual beneficial effects. However, not much literature has been published about their overlap and potential synergetic effects. The newly developed Mindfulness-Based Strengths Practice (MBSP) was among the first attempts to integrate mindfulness and character strengths. A number of preliminary studies on the effectiveness of the MBSP have been described and tested with positive outcomes such as improvement in well-being, flourishing, engagement, job satisfaction and task performance. Aims. However, no study so far has done the manipulation check on whether MBSP indeed could promote mindfulness and character strengths. The current study aims to close this gap. Method. A total of 42 participants from various job branches were randomly assigned to two conditions: (1) Mindfulness-Based Strengths Practice (MBSP); and (2) Wait-list Control. Participants’ character strengths and mindfulness were assessed before and after the intervention, and 1-, 3-, and 6 months afterward. Results. Compared to the Waitlist Control group, participants who attended an eight-week program of MBSP training showed a significant increase in mindfulness and all character strengths with the exception of the strength of spirituality and religiousness. However, when the spirituality items were separated from the religiousness items, a significant increase was present for spirituality but not religiousness. Conclusion. The current study provided support for the assumptions that (1) the MBSP training could indeed influence the cultivation of mindfulness and character strengths, and (2) spirituality and religiousness are related but distinct concepts.