Ponds in hilly region are predominantly located in low-lying valleys, often formed by the convergence of runoff from hillslopes. These ponds are to undertake the slope runoff and nutrient loss, and transported to the downstream water network of the important hydrological channel, but also hotspots for nitrogen (N) removal. However, aquaculture and land use activities in the hillslopes or within ponds significantly affect their overlying water characteristics, subsequently driving changes in denitrification mechanisms, potential, and efficiency. This study examined four types of typical ponds in the hilly region of the upper Lake Taihu: tea ponds, forested ponds, aquaculture ponds, and village ponds. Surface sediments from these ponds were collected for ¹⁵ N isotope experiments. In-situ measurements were carried out to calculate the supersaturated nitrogen concentration (ΔN₂ ), and the physicochemical properties of the overlying water were also determined to comprehensively elucidate the characteristics of N removal mechanisms, potential, and efficiency variations, and to analyze the driving factors of denitrification efficiency in different types of ponds. Results indicated that the denitrification efficiency of the tea pond was the highest (8.25%), followed by the forest pond (6.24%) and the village pond (5.90%), while the aquaculture pond exhibited the lowest (4.72%). Denitrification was the dominant N removal pathway in all pond types, with a contribution rate of 93.34%±12.59%. In contrast, anaerobic ammonium oxidationin forest ponds and tea ponds contributed a relatively high percentage of nitrogen removal, reaching more than 5%. Correlation analysis revealed that the efficiency of nitrogen removal in ponds was related to the physicochemical properties of sediments and overlying water, with differing controlling factors among pond types. Specifically, the concentrations of total nitrogen and dissolved total nitrogen were the primary factors that influenced the denitrification efficiency in forest ponds and aquaculture ponds. In contrast, the chemical oxygen demand, total suspended solids, dissolved oxygen, chlorophyll- a , and total phosphorus were identified as the main factors affecting the denitrification efficiency in village ponds. For tea ponds, no significant factors impacting denitrification efficiency were identified. For different types of ponds, managers should take measures to optimise the environmental conditions to enhance the effectiveness of nitrogen removal, which is of great significance to safeguard the clear water flow in the hilly source region.