In recent years, mindfulness meditation apps-which offer voice-guided exercises for relaxation-have been promoted as an effective tool for self-managing stress. This study examines how the type of voice-human male, human female, synthetic male, or synthetic female-can impact users' levels of relaxation, perceived usefulness, and enjoyment when following a guided meditation. Participants listened to a guided meditation and then evaluated their feelings toward both the voice and the meditation exercise. Those who listened to a human voice rated the voice as more enjoyable than those who listened to a synthetic voice. Additionally, respondents in the human voice conditions rated the meditation exercise itself as more enjoyable and useful and themselves as more relaxed than did participants guided by a synthetic voice. Finally, the effect of voice humanlikeness on perceived usefulness was significantly more pronounced with female voices. These findings suggest that naturalsounding speech is preferable for individuals completing guided mindfulness exercises. In turn, to enhance users' enjoyment and perceptions of meditation effectiveness, generated speech used in such apps should sound human-like and utilize natural speech patterns.