Coactivator-associated arginine methyltransferase 1 (CARM1) catalyzes the methylation of arginine residues of target proteins. CARM1 expression and activity are elevated during skeletal muscle atrophy. Importantly, the muscle-specific knockout of CARM1 partially attenuates the loss of muscle mass and the expression of atrophy-related genes during periods of neurogenic muscle disuse. Therefore, inhibition of CARM1 may be a therapeutic target for mitigating skeletal muscle atrophy. The purpose of this study was to determine the effectiveness of EZM2302 (EZM; Epizyme, Inc.), a novel, orally bioactive, specific CARM1 inhibiting compound, at repressing CARM1 activity in skeletal muscle. We utilized 3-month-old male and female mice (n = 3/sex) that were housed and cared for in accordance with Canadian Council for Animal Care guidelines. Mice were treated with either 150 mg/kg EZM or vehicle (Veh) via oral gavage BID for either 2, 4, or 8 days. Tissues were collected 6 hours following the final dose and muscle mass was recorded. Western blotting was performed to evaluate protein expression in the tibialis anterior (TA) muscle and liver. To assess CARM1 activity, we investigated the arginine methylation status (i.e., the methylated form of the protein relative to its total amount) of known CARM1 substrates BAF155 and PABP1, as well as the myocellular level of arginine methylated proteins preferentially targeted by CARM1. At this time, we observed similar outcomes between males and females so the data were collapsed by sex (n = 6). EZM significantly reduced BAF155 methylation status in the TA muscle by 72-80% between 2-8 days of treatment relative to the Veh-treated group. EZM also attenuated (p < 0.05) muscle PABP1 methylation status by 65% and 58% after 4 and 8 days of treatment respectively. Similarly, arginine methylation of CARM1-specific substrates across all muscle proteins was reduced by ~50% (p < 0.05) between 2-8 days of EZM administration. The attenuation of BAF155 and PABP1 methylation status, as well as arginine methylated CARM1-specific substrates, was greater in liver as compared to muscle. Skeletal muscle mass, including the TA, quadriceps, triceps, and extensor digitorum longus, in the EZM-treated mice were similar to Veh-treated mice at all time points. Collectively, these results suggest that EZM is effective at significantly inhibiting CARM1 activity in skeletal muscle. Future work in our laboratory will examine the efficacy of EZM in attenuating the loss of muscle mass and function during atrophy-inducing conditions.