Oxytocin is a neuropeptide that has potential for the development as an anti-alcoholism treatment. Clinical studies have recently found that intranasal oxytocin treatment reduces alcohol withdrawal symptoms or craving in alcohol-dependent patients with high anxiety. In rodents, activation of oxytocin receptor by systemic or central administration of oxytocin decreases alcohol reward, consumption and cue-induced alcohol seeking behaviors. The neurobiological interaction between oxytocin and mu-opioid receptors (MOR) has been well established: MOR agonists or endogenous beta-endorphin inhibit oxytocin release and neuronal activity. Here we explored whether oxytocin under MOR antagonism by naltrexone can enhance the reduction of alcohol intake by oxytocin alone after 3-week excessive alcohol drinking in an intermittent access alcohol (IAA) mouse model or after 1-week abstinence in mouse alcohol deprivation effect (ADE) model. For a genetic control for naltrexone effect, neuronal proopiomelanocortin enhancer (nPE) knockout mice with brain-specific beta-endorphin deficiency were further studied with oxytocin. We found that administration of oxytocin at 0.1 mg/kg [but not 0.01 or 0.03 mg/kg] decreased alcohol intake and preference. When oxytocin co- administered with naltrexone, oxytocin at 0.01-0.03 mg/kg with low doses of naltrexone (0.5 or 1 mg/kg) reduced alcohol drinking more profoundly than the sub-effective doses of oxytocin alone. Alcohol “relapse” in the ADE was prevented by either oxytocin alone or co-administration of oxytocin with naltrexone. The oxytocin effect was confirmed in nPE-/- mice, suggesting independent mechanisms by which oxytocin and naltrexone reduced alcohol drinking. Our study suggests that oxytocin in combination with low-dose naltrexone offers a novel strategy in alcoholism treatment.