【Objective】 Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are the two competing nitrate reduction pathways that remove the available nitrate, both of which are affected by inter-related environmental factors. Understanding how environmental factors regulate nitrate partitioning in these two competing processes is of great significance for the optimization of nitrogen management in paddy fields.【Method】 Using ¹⁵N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), a series of laboratory incubation experiments were performed to investigate the effects of different environmental factors including temperature (5, 15, 20, 25, and 35 ℃), pH (5, 6, 7, 8.5, and 9.5), NO₃^– concentration (50, 100, 150, 200, and 300 µmol·L^–1), C/N (0, 2.5, 5, 12, and 30), Fe²⁺ (0, 300, 500, 800, and 1 000 µmol·L^–1), and S^2– (0, 50, 62.5, 100, and 125 µmol·L^–1) on denitrification and DNRA rates and their partitioning in nitrate reduction in three paddy soils (Wuchang, WC; Changshu, CS; Ya’an, YA). 【Result】 Denitrification was the predominant pathway (87.97% – 91.73%), whereas DNRA only contributed to 8.27% – 12.03% of the total dissimilatory nitrate reduction in all treatments. Denitrification and DNRA rates increased exponentially with increasing temperature, as well as the DNRA/(Denitrification + DNRA) (R_DNRA). The highest denitrification and DNRA rates occurred at the pH of 7 and 8.5, respectively, and R_DNRA was higher in an acidic environment (6.24%–15.56%) than under an alkaline environment (4.92%–14.67%). The response of denitrification and DNRA rates to nitrate concentrations fitted well with the Michaelis-Menten relationship, in which the V_maxand K_m of denitrification were larger than those of DNRA. In the three paddy soils, compared with the treatment without glucose addition, denitrification rates were significantly increased by 22% – 35% at the C/N ratio of 2.5. Following the C/N ratio increased to > 2.5, DNRA rates were enhanced by 74% – 199%. In terms of Fe²⁺and S^2– addition treatments, denitrification rates were the highest in the low levels of electron donors (300 – 500 µmol·L^–1 Fe²⁺ and 50 – 62.5 µmol·L^–1 S^2–), whereas more electron donors (800 – 1 000 µmol·L^–1 Fe²⁺ and 100 – 125 µmol·L^–1 S^2–) were required when DNRA reached the peak rates. 【Conclusion】 By exerting different effects on rates of denitrification and DNRA, temperature, pH, NO₃^–, C/N ratio, Fe²⁺, and S^2– concentration significantly changed the partitioning between denitrification and DNRA. Specifically, relatively high temperature, C/N, Fe²⁺, and S^2– concentration favored nitrate partitioning to DNRA, while denitrification dominated the nitrate reduction process in environments with a relatively high NO₃^– concentration. Collectively, our results provide comprehensive information in terms of regulation of environmental factors on nitrate partitioning between DNRA and denitrification in paddy soils. This deepens our understanding of nitrate reduction processes and provides a scientific basis for increasing nitrogen use efficiency by favoring the nitrate partitioning to DNRA in rice fields.