Background: The use of psychoactive substances is common among commercial drivers, and it has been implicated as a major cause of road accidents. In order to effectively control its use among this population group, the correlates must be well understood. Previous studies have examined physical and sociodemographic factors as correlates of substance use among commercial drivers, but few if any have assessed the psychological factor of personality traits as correlates of substance use among commercial drivers, especially in Ekiti state. Objective: To assess the psychological factor of the Big- Five personality traits associated with substance use among commercial drivers in Ekiti State, Nigeria Method: It was cross-sectional descriptive study, carried out in 14 motor parks spread across 3 local governments with the highest traffic flow and concentration in Ekiti. Using a multi-stage purposive random sampling method, 422 intra-state commercial drivers were interviewed using an adapted WHO Student’s Drug Use questionnaire and a 44-item Big Five Inventory. Results: Most of the respondents fall within 30-49years which constituted 63% of their population. The overall prevalence of substance use was 91.5% (ever use), 82.0% (use within 12mths) and 80.6% (current users). The correlates of substance use includes; Alcohol- marital status, religion, and the Big-Five factors of Agreeableness and Neuroticism; Cannabis- age, marital status, education, religion and Big-Five factors of Openness, Extraversion and Neuroticism; Cigarette- all sociodemographic factors (except tribe) and Big-Five factors of openness and agreeableness; Cocaine- age, marital status, tribe and religion; Amphetamine- age duration of driving and Big-Five factors of Conscientiousness and Extraversion; Opioids-Age and education; Sedatives- Education, duration of driving ,Agreeableness and Neuroticism. Conclusion: The Big-Five personality traits and sociodemographic factors are important correlates of substances use among commercial drivers, and public health interventions and treatment plans should be tailored towards individual personality traits