Objective: The use of opiate substances, such as heroin and methadone, has been proven to cause executive function damage. The extent of damage may be mediated by the activity of enzyme aldehyde dehydrogenase 2 (ALDH2), which plays an important role in neurotransmitter dopamine metabolism. The single nucleotide polymorphism Glu487Lys distributes mostly in Asia and codes for ALDH2 with greatly reduced enzyme activity. The current study aims to explore the effect of ALDH2 on executive function in opiate users. Methods: A total of 94 opiate users were recruited and 58 patients finished the neuropsychological assessment and blood genotyping. Results: After co-variating the influence of age and the years of education, we found that participants with ALDH2 A allele performed worse on the Category Complete index of the Modified Wisconsin Card Sorting Test (F = 5.34, p = 0.02), suggesting an impaired planning ability in this group. We also found that ALDH2 A carriers went through the Trail 2 in Color Trails Test faster (F = 8.21, p = 0.01), in part suggesting better set-shifting abilities; however, impulsiveness and lack of planning associated with this study group may also explain the faster performances. Conclusions: The role that ALDH2 plays in the pathology of cognitive impairment in opiate users may lead new focus in studies of the pathophysiology in opiate usage and its consequences on cognitive function.