This research was carried out to assess mothers’ knowledge and attitude on prevention of malaria among under (5) years children in selected primary health centers in Lagos State. The objectives of this study were to determine their current level of knowledge and skills in term of disease identification, management and transmission of malaria; evaluate the effectiveness of insecticide-treated net in the prevention of malaria among them; assess their knowledge on the use of Artemisinin-based combination therapy (ACT) in the treatment of malaria; and evaluate the factors affecting them in the prevention of malaria among under-five children. A simple random sampling technique was used in selecting eighty-seven (87) caregivers, but only eighty-four (84) of them were validated for the study. A self- developed questionnaire served as the primary instrument of data collection for the study,data collected were analyzed and presented on frequency/percentage tables, and bar chart(s) using Statistical Package for Social Sciences (SPSS) version 25 and Microsoft Excel version 2010. The findings revealed that they exhibited an overall good level of knowledge, positive attitude, and good level of practice of malaria prevention among under-five children. The assessment of factors affecting in prevention of malaria among under-five children revealed that majority (88.1%) are married; 71.4% live in urban area; 64.3%are Christians; 59.5% self- employed; 52.4% have child who is not under five years of age; 47.6% have tertiary level of education; 40.5% have an under-five child; while 33.3% are 26-30 years of age. The study found significant relationship between the mothers’ knowledge and attitude towards prevention of malaria among under-five children (p < .05). Based on these findings, the study concluded that there is need to ensure consistency and improve their practice of malaria prevention through proper evaluation and amelioration of their knowledge and attitude towards prevention of malaria among under-five children.