Smartphone addiction connotes excessive and repetitive use of smartphone on a daily basis. It is a destructive behaviour that has capacity of affecting an individual negatively in his/her physical and mental health, relationships, productivity and academic performance. The organismic variables that could dictate the severity of this addiction include gender, age, school factors, peer influence, parental socio-economic status among othersThis paper therefore, examined effects of Demographic factors on Smartphone addiction of students in a Nigerian University. Three hypotheses were formulated to guide the research. The sample consisted of one hundred and ten (110) students randomly selected from Lagos State University (LASU). A 15-item questionnaire titled Smartphone Addiction Scale(SPAS) was designed for data collection. Cronbach’s Alpha reliability coefficient of the instrument stood at 0.82. The study adopted the descriptive survey design to seek information. Data analysis was carried out with the use of t-test and ANOVA. Results showed that there is a significant effect of age on smart phone addiction of students in a Nigerian University. The results also revealed that their smart phone addiction is not gender based, neither does it depended on their type of school. Counsellors, parents and teacher should watch out for various signs of smartphone addiction and properly guide the students on the right path.