Western Boreal Plain peatlands can play an important role in the global nitrogen cycle by storing N in peat and potentially releasing large amounts of N to the atmosphere. In this study, biological denitrification rates were measured in marsh and fen vegetation zones in two boreal peatland-pond complexes in northcentral Alberta, Canada. Assuming negligible winter denitrification, we estimated annual denitrification rates of 11 g N·m⁻² in marshes and 24 g N·m⁻² in fens. Two techniques were employed to measure denitrification: 1) measurements of direct N₂-flux were taken from intact cores in gas-tight N-free chambers, and 2) nitrous oxide (N₂O) flux was measured in the two fens using in situ chambers. N₂ fluxes ranged from 2.14–4.19 mg N·m⁻²·h⁻¹ in marshes and 6.19–6.81 mg N·m⁻²·h⁻¹ in fens. N₂O release from fen peat ranged from consumption to 0.025 mg N·m⁻²·h⁻¹. Peat with higher carbon and moisture content was a source of N₂O whereas peat with lower carbon and moisture content was a sink. Surface water did not appear to be a major source of nitrate for denitrification. However, denitrification rates were positively correlated with peat extractable nitrate. Combined with mineralization studies, this indicated that soil nitrification provided most of the substrate for denitrification.