Butyrylcholinesterase (BChE), a serine hydrolase, is found in many mammalian tissues, such as serum and central nervous system. Although its natural substrate is unknown, plasma esterase BChE has many important biological functions, such as detoxifying roles against cocaine toxicity. BChE is present in human plasma at a significant concentration (5 mg/L, corresponding to 60 nM). The endocannabinoid arachidonoylethanolamide (anandamide, AEA) and other acylethanolamides (NAEs) such as palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) are almost ubiquitary molecules and are physiologically present in many tissues, including blood and brain, where they show neuroprotective and anti-inflammatory properties. Our results indicate that physiological concentrations of NAEs inhibit both not isolated and isolated human plasma BChE significantly (Ki in the range 1.32–7.48 nM), suggesting a possible in vivo modulation of the physiological roles of BChE by the endogenous molecules AEA, PEA and OEA. The NAEs inhibitory action on BChE could open new perspectives for the consequences of their presence (both in plasma and in other districts of human body, such as in brain) on the biological and pharmacological roles of BChE. NAEs plasma levels could affect cocaine degradation by BChE, suggesting the opportunity to consider this possibility both in the treatment of cocaine abuse and in the possible use of BChE as therapeutic enzyme.