This study was conducted to assess the impact of the mobile phones among secondary school students in Morogoro municipality. Specifically the study determined the influence of mobile phones on students’ behaviors, and assessed the impact of mobile phones on students’ academic performance. A cross sectional research design was used to obtain data from both primary and secondary sources of information through structured questionnaire from 90 respondents obtained through simple random sampling. The collected data were coded and analyzed by using Statistical Package for Social Science (SPSS) computer program. Findings revealed that, 93.3% of the interviewed respondents’ access and use mobile phones, and 63.3% agreed that mobile phones usage among secondary school students cause behavioural changes. Also the study revealed that students use mobile phones to organize and maintain their social networks (8.9%), search materials on internet and organize discussion (54.4%), and informing their parents’ on issues concerning their education (1.1%). A number of impacts on using mobile phones were revealed, including; facilitating engagement of students in sexual affairs (41.1%), decline in moral values (43.3%), decrease in academic performance (91.1%), causing health problems to students (50.0%), cause disturbance in studies (47.8%) and resulting to time wasting (88.9%). This study recommends various measures to be taken by secondary school teachers and parents to minimize the use of mobile phones among secondary school students hence ensuring that students are getting time to concentrate on their studies and improve academic performance.