Treatment of nanofiltration concentrate (NFC) from landfill leachate is challenging due to its complex composition and high concentration of refractory organic matter. This study proposed a combined process of ozone pretreatment and partial denitrification/anammox (PD/A) for treating NFC, exploring the feasibility of using ozone-oxidized NFC as a carbon source for partial denitrification. The ozone oxidation process was employed to degrade the refractory organic compounds. With an ozone flow rate of 1.2 L/min and a reaction time of 50 min, the chemical oxygen demand (COD) removal efficiency of NFC was 20.83%, and the volatile fatty acid (VFA) content reached a maximum value of 104.37 mg/L. Meanwhile, the process significantly increased the ammonia and nitrate concentrations in the NFC. Then, PD/A process was applied to remove nitrogen from the NFC. Results showed that PD/A can effectively remove nitrogen from the NFC without additional carbon source. Using VFA produced in the ozone oxidation stage as carbon source, the reactor achieved a nitrogen removal efficiency of approximately 70%, resulting in an effluent with a total nitrogen below 40 mg/L, which satisfied the relevant standards in China. This study provides new insights into the application of ozone oxidation and PD/A in treating NFC from leachate.