The study sought to establish the relationship between school social environment and psychological wellbeing among learners in Junior Schools in Tharaka Nithi County, Kenya. It adopted descriptive survey and correlational research designs. Multistage sampling was used to select 377 respondents comprising of 328 grade 8 learners, 42 grade 8 class teachers and 7 Sub- County Quality Assurance and Standards Officers. Psychometric test instrument, questionnaires and interview schedules were used to collect data from sampled respondents. Reliability of the instruments was ascertained through Cronbach analysis of data obtained from a pilot study carried among 53 respondents sampled from the same study area but who were not involved in the actual study. Data was collected from 325 grade eight learners, 41 grade eight class teachers and 5 Sub-County Quality Assurance and Standards Officers (SQASO) in Tharaka Nithi County giving the study a return rate of 98.41%. Qualitative data obtained was analyzed thematically while quantitative data was analyzed descriptively and inferentially with the aid of the Statistical Packages for Social Sciences (SPSS) version 27.0 computer software. Frequencies and percentages were used to describe the existing relationship between the variables while hypothesis was tested using regression analysis at 95% level of significance. The study established that a positive social relationship between among peers and positive interactions between learners and teachers catalyze the social environment which promotes junior school learners psychological wellbeing. It concluded that the school’s social environment is negatively and significantly related to the psychological wellbeing of junior school learners.The study recommended that management of public junior school in collaboration with other education stakeholders launch and monitor turn-around initiatives aimed at fostering quality school social environment for learners’ improved psychological wellbeing. Areas of focus could include workshops on peer relations, stress management techniques, seminar on teacher-learner interaction, problem-solving techniques, and goal-setting for social and academic success could be part of the initiatives.