Functionalized polyamide 6 (PA 6) filament fabric with excellent thermal stability and UV resistance was copolymerized with methyl methacrylate (MMA) via in-situ grafting initiated by immobilized ascorbic acid and hydrogen peroxide. Grafting modification process was determined at 30 % of H2O2, at 70 °C for 60 min of duration, and the grafting degree could be tuned by adjusting the amount of MMA. Microscopic investigations confirmed the granular MMA was immobilized on the surface of PA 6 fibers. A strong peak at 1729 cm−1, assigning to CO stretching of ester bond of MMA, demonstrated MMA was successful grafted. The decomposition temperature of grafted PA 6 occurring at 444.6 °C, was 40 °C higher than that of pristine PA 6 (403.4 °C). Additionally, the introduction of MMA also improved the UV resistance of PA, more than 80 % decrease in transmittance of UVA band and UVB band with only 0.34 % grafting degree. Therefore, it can be concluded that in-situ grafting of MMA can endow PA 6 with excellent thermal stability and UV resistance. We believe that in-situ grafting of MMA would have important guiding significance for the fabrication of PA 6 based textiles with excellent thermal stability and UV resistance. Display omitted •Functionalized PA6 was copolymerized with MMA via in-situ grafting initiated by immobilized H2A and H2O2 in aqueous solution.•The grafting degree can be tuned by the amount of MMA and the process parameters of in-situ grafting.•Thermal stability of grafted PA6 was promoted greatly with the Td 40 °C higher than that of pristine PA 6.•UUV resistance of grafted PA 6 was enhanced dramatically.