Objectives Tai Chi Chuan (TCC) is a common mindfulness-based aerobic exercise. However, the evidence on the effects of TCC practice on mindfulness has been controversial. The aim of this study was to explore whether TCC practice with an emphasis on interoceptive awareness could improve mindfulness levels in a healthy adult population. Methods Sixty-one healthy adults without mind-body practice experience were divided into the TCC and control groups. Participants in the TCC group received classic Yang-style supervised TCC practice for 8 weeks, whereas those in the control group did not receive any intervention. The Five Facet Mindfulness Questionnaire and Multidimensional Assessment of Interoceptive Awareness were administrated at baseline, the end of week 8, and the end of week 24. Results In terms of mindfulness, significant interaction between group and time was found in describing, acting with awareness, nonjudging, and nonreactivity. For interoceptive awareness, there were marginally significant interaction effects of time and group in attention regulation, self-regulation, and trust. TCC practice significantly improved the above-mentioned dimensions of mindfulness and interoceptive awareness. Moreover, we still observed increased describing, acting with awareness, and nonjudging in mindfulness, and trusting in interoceptive awareness for the TCC group at the end of week 24. Conclusions This study indicated that 8-week TCC practice with a component of interoceptive awareness could increase mindfulness levels, which could still be observed in the 24th week. These findings are of great significance for health practice and treating emotional disorders utilizing mind-body practice as an alternative and complementary medicine.