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Lytic polysaccharide monooxygenases (LPMOs) can improve the effectiveness with which agricultural waste is utilized. This study described the potent AA9 family protein Ms LPMO3, derived from Morchella sextelata. It exhibited strong binding to phosphoric acid swollen cellulose (PASC), and had the considerable binding ability to Cu2+ with a K d value of 2.70 μM by isothermal titration calorimetry (ITC). Ms LPMO3 could also act on PASC at the C1 carbon via MALDI-TOF-MS results. Moreover, Ms LPMO3 could boost the hydrolysis efficiency of corncob and wheat bran in combination with glycoside hydrolases. Ms LPMO3 also exhibited strong oxidizing ability for 2,6-dimethoxyphenol (2,6-DMP), achieving the best V max value of 443.36 U·g−1 for pH 7.4 with a H 2 O 2 concentration of 300 µM. The structure of Ms LPMO3 was obtained using AlphaFold2, and the molecular docking results elucidated the specific interactions and key residues involved in the recognition process between Ms LPMO3 and cellulose. Altogether, this study expands the knowledge of AA9 family proteins in cellulose degradation, providing valuable insights into the mechanisms of synergistic degradation of lignocellulose with cellulases. • Ms LPMO3 was a novel AA9 family protein and could tightly bind with copper ions. • Ms LPMO3 possessed strong oxidizing ability for 2, 6-DMP. • Ms LPMO3 could oxidize PASC at the C1 site. • Ms LPMO3 exhibited synergistic effects on natural substrates with glycoside hydrolase. [ABSTRACT FROM AUTHOR]