The smartphone has been used widely in daily life for communication, business, security and writing. Nevertheless, studies of smartphone product design influences on handedness are quite limited. The objective of this study is to investigate the handedness effect of unilateral (right hand) and bilateral (both hands) typing task using a smartphone on hand muscle activities. Six participants ranging from 23 – 26 years old with minimum of 2 years of experience using the smartphone performed typing task. The surface electromyogram (sEMG) signal of External Carpi Radialis (ECR), Biceps Brachii (BB) And Trapezius (UT) from both right and left hands were recorded during the typing task of 3 minutes with 10 seconds rest interval. The percentage of Maximum Voluntary Contraction (%MVC) of unilateral typing method is higher as compared to both hands typing method. The comparison of left and right hand when both hands typing showed that the left-handed (LH) participants having high muscle activities on the left hand while for righthanded (RH) participant, all muscle activities were higher on the hand. In conclusion, the study confirms that the usage of a smartphone using one hand is prone to more fatigue compare using both hands. Besides, non-dominant hand user also showed higher muscle activation of the same muscle with dominant hand users. This means faster fatigue condition for the non-dominant users in the one-handed typing method.