Fatigue is a pathological state that can impair physical and cognitive performance, making the development of effective therapeutic strategies crucial. In this study, an acid polysaccharide (MHa) was isolated from Mentha haplocalyx. Structural analysis showed that MHa (40.7 kDa) has a backbone consisting of 4-α-GalAp, 6-α-Galp, and 4,6-α-Galp, with branches at the C6 of 4,6-α-Galp linked to four distinct side chains, including 4-α-Galp, 3,6-β-Manp, t-α-Araf, t-α-Rhap, t-α-Glcp, and t-β-Rhap. MHa possesses a triple-helix conformation with a sheet-like appearance, which may contribute to its biological stability and activity. Functionally, MHa exhibited significant antifatigue effects, with the 400 mg/kg dose showing the most potent activity. Compared to the model group, treatment with 400 mg/kg of MHa increased the exhaustive swimming time by 1.89-fold in fatigued mice, reduced blood lactate and urea nitrogen levels by 24.21 % and 35.57 %, respectively, and enhanced liver glycogen, muscle glycogen, and ATP levels by 20.08 %, 46.52 %, and 50.43 %, respectively. MHa improved the activities of Ca