Introduction: Smartphone addiction is a hotly debated public health issue and it affects every generation especially the youth and younger generation nowadays (Generation Z / i-Generation) and contributes to the poor mental health status like stress, anxiety and depression. This study is carried out to determine the prevalence of smartphone addic-tion and its association with stress, anxiety and depression among the undergraduate students in Unitversity Malaysia Sabah. Methods: A cross-sectional study was conducted among the undergraduate students in Universiti Malaysia Sabah. A total number of 456 undergraduate students in Universiti Malaysia Sabah with at least a smartphone device were enrolled in the study by stratified random sampling. A self-administered questionnaire, Smartphone Addiction Scale Malay Version (SAS-M) and The Depression, Anxiety and Stress Scale – 21 Items (DASS-21) Malay Version were used for data collection. The prevalence of smartphone addiction, stress, anxiety and depression among un-dergraduate students of Universiti Malaysia Sabah were determined. Simple linear regression was used to determine the effect of smartphone addiction to stress, anxiety and depression. Results: Prevalence of smartphone addiction among undergraduate students in Universiti Malaysia Sabah is 61.2% (95% CI : 56.5%, 65.7%). The prevalence of stress, anxiety and depression among undergraduate students in Universiti Malaysia Sabah are 34.9%, 58.6% and 42.5% respectively. The univariate analysis shows that smartphone addiction is significantly associated with stress (Regression Coeeficient = 0.774, 95% CI 0.54, 1.01 ; P-value <0.001), anxiety (Regression Coeeficient = 0.647, 95% CI 0.402, 0.892 ; P-value <0.001) and depression (Regression Coeeficient = 0.576, 95% CI 0.344, 0.808 ; P-value <0.001). Conclusion: This study shows that there is a high prevalence of stress, anxiety and depression among un-dergraduate students in Universiti Malaysia Sabah as compared to the statistics from National Health and Morbidity Survey 2017. This study demonstrates the significant association between smartphone addiction with stress, anxiety and depression. Interventions shall be implemented with the identification of the smartphone addiction as the risk of poor mental health problem.