The majority of research on yoga focuses on its psychophysiological and therapeutic benefits, while the spiritual aspects are rarely addressed. Changes of specific aspects of spirituality were thus investigated among 160 individuals (91% women, mean age 40.9 ± 8.3 years; 57% Christians) starting a 2-year yoga teacher training. We used standardized questionnaires to measure aspects of spirituality (ASP), mindfulness (FMI-Freiburg Mindfulness Inventory), life satisfaction (BMLSS-Brief Multidimensional Life Satisfaction Scale), and positive mood (lightheartedness/relief). At the start of the course, scores of the respective ASP subscales for search for insight/wisdom, transcendence conviction, and conscious interactions/compassion were high, while those for religious orientation were low. Within the 6 month observation period, both conscious interactions/compassion (effect size, Cohen's d = .33), Religious orientation (d = .21), Lightheartedness/Relief (d = .75) and mindfulness (d = .53) increased significantly. Particularly non-religious/non-spiritual individuals showed moderate effects for an increase of conscious interactions/compassion. The results from this study suggest that an intensive yoga practice (1) may significantly increase specific aspects of practitioners' spirituality, mindfulness, and mood, (2) that these changes are dependent in part on their original spiritual/religious self-perception, and (3) that there are strong correlations amongst these constructs (i.e., conscious interactions/compassion, and mindfulness).