Phosphorus (P) is an essential nutrient for plant growth in subtropical forest soils. Altitude gradient might modify the soil-plant-microorganisms system and affect P forms and availability. Therefore, it is critical to understand the characteristics of soil P fractions at different altitudes for maintaining the sustainable development of mountain forest ecosystems. Soils were analyzed for P fractions, microbial community composition, and activities of acid phosphomonoesterase (ACP) and phosphodiesterase (PD) in Pinus taiwanensis Hayata forests at different altitudes (1300 and 1600 m) in Daiyun Mountain. The results revealed that the altitudinal gradient studied had a significant effect on soil P factions. Soil total P content decreased by 48.4%-49.8% at 1600 m compared to 1300 m altitude. All P fractions of labile P, moderately labile P, and non-labile P also significantly decreased by 45.7%, 58.6%, and 38.7% in the A horizon, and by 82.6%, 59.9%, and 31.1% in the B horizon, respectively. Furthermore, significant changes occurred between 1300 and 1600 m above sea level, as the soil at higher altitudes showed lower activities of phosphodiesterase and phospholipid fatty acids (PLFAs) of all microbial communities than those of the soil at lower altitudes. Conversely, activities of acid phosphomonoesterase showed an increasing trend. Redundancy analysis (RDA) indicated that the changes in P fractions were mainly driven by soil organic carbon (SOC); moreover, soil organic P (NaHCO₃-Po and NaOH-Po) was positively correlated with SOC. In addition, phosphatase and ectomycorrhizal fungi (EMF) were important factors affecting changes in P fractions of the soil. Our study indicated that altitude had an effect on the accumulation of soil organic matter and microbial community composition and function, which affected soil P availability and cycling.