The study aimed to determine the effects of a 4-month Tai Chi intervention on tenderness, functional capacity, symptomatology, and quality of life in men with fibromyalgia. The effect of a 3-month detraining period was also analyzed. Six men with fibromyalgia (age 52.3 ± 9.3 years) followed a 4-month Tai Chi intervention. The outcome variables were tenderness, functional capacity (30-second chair stand, handgrip strength, chair sit and reach, back scratch, blind flamingo, 8 feet up and go, and 6-minute walk tests), and self-administered questionnaires. A significant improvement (p = .028) after the intervention period for the chair sit and reach test was found, such improvement was maintained after the detraining phase. Tenderness, symptomatology, and quality of life did not significantly change after the intervention period or the detraining phase. In summary, a 4-month Tai Chi intervention improved lower body flexibility in men with fibromyalgia. This improvement persisted after the detraining period.