OBJECTIVE: This study aims to explore the effects of 24 weeks of three-duration Tai-Chi (TC) practice on depression and sleep quality in older women. METHODS: A total of 124 older women were randomly divided into four groups: short-time group (SG, n = 31, mean age: 65.3), medium-time group (MG, n = 30, mean age: 65.7), long-time group (LG, n = 32, mean age: 64.9) and control group (CG, n = 31, mean age: 66.2). The Beck Depression Inventory (BDI) and Pittsburgh Sleep Quality Index (PSQI), and serum levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and 5-hydroxytryptamine (5-HT) were measured. RESULTS: 1) Within-group comparisons: Compared with the baseline, the 12th and 24th weeks showed reductions in TNF-α and IL-6 levels and increase in 5-HT level in the SG, MG and LG (p < 0.05). The LG at the 24th week had reduced BDI and PSQI scores (p < 0.05). Compared with the 12th week, the 24th week showed reductions in TNF-α and IL-6 levels (p < 0.01) and increase in 5-HT level (p < 0.05) in the SG, MG, and LG. 2) Between-group comparisons: The SG, MG, and LG had lower TNF-α and IL-6 levels and higher 5-HT level than the CG at 12th and 24th weeks (p < 0.05). At the 24th week, the LG had lower BDI and PSQI scores than the CG and lower TNF-α level than the SG and MG (p < 0.05). The MG had lower TNF-α levels than the SG in the 24th week (p < 0.01). CONCLUSION: These results indicate that older individuals may undertake at least 12 weeks of TC exercise with a duration of 60 min per session to significantly improve depressive mood and sleep quality.