Surviving life on the streets is undeniably challenging and takes a toll on the psychosocial well-being of street children, often leading to substance use. This study aimed to investigate the correlation between psychosocial health and drug use among street children in Starehe Sub-County, Nairobi County, Kenya, utilizing the Problem Behavior Theory (PBT). Employing a correlational research design, data were collected from a sample of 100 street children, selected through cluster and simple random sampling from a target population of 30,000 in Starehe Sub-County. Additionally, information was gathered from four officials at the Starehe Children’s Office, eight officials from NGOs/FBOs operating in the sub-county, one sub-county administrator, and four ward administrators. The qualitative data obtained through questionnaires were analyzed using descriptive statistics such as mean, percentage, and frequencies, along with inferential statistics like Pearson correlation and regression analysis. The presentation of findings utilized charts and tables, while qualitative interview data underwent thematic analysis and were presented in a narrative format. The study's outcomes revealed a noteworthy impact of psychosocial health on drug use among street children, with a significant correlation between the two (r=0.503). The findings suggested that interventions aimed at improving the mental health of street children had a meaningful effect on reducing drug use. Recommendations stemming from the study include the necessity for providing homes to street children to mitigate exposure to stressful conditions leading to mental health issues. Furthermore, the study proposed the implementation of regular free mental healthcare clinics for all street children and emphasized the importance of awareness campaigns to educate them on the detrimental consequences of drug use. Strengthening behavioral counseling, support groups, and creating sober social networks for street children were also highlighted. The study advocated for government and non-governmental organizations to develop programs supporting access to counseling services and training certain street children to provide peer counseling to their fellow youths.