Background: Cannabis use is common among patients with opioid use disorder receiving methadone treatment. Research has shown that cannabis use during methadone treatment may impact negatively on treatment outcome. This study aimed at determining the prevalence and pattern of cannabis use and the associated socio-demographic characteristics among patients on methadone treatment. Methods: This was a retrospective study of 984 patients on methadone therapy at a methadone maintenance treatment clinic in Nairobi, Kenya. Data on socio-demographic characteristics and drug use patterns based urine drug screens was collected from patients’ files. Data was analyzed using SPSS for windows version 23.0. Results: Prevalence of cannabis use was 84.8% at baseline and 62.8% during follow up. Polysubstance use pattern was observed with heroin, cannabis and benzodiazepines being the commonest drugs. Majority of cannabis users were male (88.1%), aged 28-37 years (42.2%), unemployed (74.3%), had low level of education (87.7%) and single (72.4%). Cannabis use was associated with loss to follow up (p<0.001). Females were more likely to drop out of treatment and less likely to stop using cannabis during follow up compared to males. Sociodemographic factors associated with reduced risk for cannabis use were; being in older age group 48-57 years (OR 0.51, 95%CI, 0.30-0.87, p=0.013) and university education (OR 0.15, 95%CI, 0.05-0.69, p=0.005) while being in age group 18-27 years and being married were associated with increased risk for cannabis use (OR 2.62,95%CI, 1.78-3.86,p=0.001 and OR 1.50, 95%CI, 1.7-2.10,p=0.021 respectively). Conclusion: There is a prevalence of cannabis use among patients in receiving methadone treatment in Kenya is similar. In addition, cannabis use was associated with loss to follow up and sociodemographic characteristics. Cannabis use screening and targeted interventions for management should be incorporated in methadone treatment programs to improve outcomes for patients on methadone. Key words : cannabis, opioid use disorder, methadone maintenance treatment, Kenya