Type 2 diabetes mellitus (T2D) is a chronic metabolic disorder characterized by hyperglycemia and insulin resistance, which the CDC estimates currently afflicts one in ten U.S. adults and is projected to continue to rise sharply over the next 50 years. Acyl peptide enzyme hydrolase (APEH), an enzyme circulating in peripheral blood, has been implicated in rodent models of diabetes. To understand if APEH is affected in diabetes, the APEH activity was measured in the blood serum of patients with T2D compared to age-matched controls. Our results show that APEH activity is 22% lower (p = 0.0163) in T2D patients compared to matched controls. Importantly, there was no observable difference in APEH protein expression between cohorts, suggesting that APEH activity is regulated at the protein level. This work is important as it contributes to our knowledge of T2D and the role of APEH in human disease.