To investigate the effects of straw residues with reduced nitrogen (N) fertilizer on greenhouse gas (GHG) and N losses in paddy fields, we conducted a field experiment during two growing seasons in paddy rice systems in southern China to evaluate the impacts of the application of straw residues with reduced N fertilizer on rice yield, GHG emissions, and ammonia (NH₃) volatilization. The four treatments included N100 (conventional dose of N fertilizer), SN100 (conventional dose of N fertilizer + straw), N60 (60% of the conventional dose of N fertilizer), and SN60 (60% of the conventional dose of N fertilizer + straw). We found that the yield of the SN60 treatment was slightly reduced, but the partial factor productivity of applied N (PFP_N) was significantly increased by 63.9% compared to the N100 treatment. At the same N application rate, the application of straw increased soil organic C (SOC), methane (CH₄) emissions, carbon dioxide (CO₂) emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), and net ecosystem carbon budget (NECB), but significantly decreased soil N₂O emissions and NH₃ volatilization. Compared with conventional fertilization (N100), straw residues with reduced N fertilization (SN60) reduced N₂O emissions and NH₃ volatilization by 42.1% and 23.9%, and increased GHGI and NECB by 11.1% and 18.3%, respectively. The results indicate that straw residues with reduced N fertilizer are a feasible strategy to reduce N losses in paddy fields while increasing carbon sequestration.