Mental stress is used broadly to refer to the negative emotional, behavioural, and biological response to a perceived threat. Yoga is useful for cultivating mindfulness and reducing stress. A study was undertaken among a random sample of 40 adult yoga practitioners in Kozhikode, Kerala, India before and after practicing yoga to analyse the influence of yoga on the mental stress of the practitioners using an interview schedule containing the Perceived Stress Scale (Cohen et al, 1983), the respondent’s age, sex and period of yoga practice. The stress score was computed as the total of the item scores in the scale. The data was analysed statistically. The results show that yoga contributes to up to about two times less mental stress for the respondents, when compared to before yoga practice. Women experience lower stress than men through yoga practice. A higher period of yoga practice is found to reduce the level of stress. Age showed no statistically significant influence on the stress score of the practitioners. It has been observed from the study that, in addition to less of negative emotions, yoga practitioners experience more of positive emotions also, which contribute to less stress for them observed in this study. Linear regression analysis showed that the