Purpose The study aims to determine the effects of smartphone use on the trunk muscle activity while walking in young students. Methods Twentyone subjects were asked to perform 10meter walk test between upright walking without using a smartphone and conducting twohanded texting while walking with using a smartphone, and the electromyography activities of the trunk were quantified. When using a smartphone, cervical flexion angle was measured using the digital goniometer. Results First, middle trapezius, latissimus dorsi, and external abdominal oblique muscles decreased muscle activity when walking by texting to the smartphone than when walking without using the smartphone (p<0.05). The upper trapezius muscle activity increased when walking by sending text messages with a smartphone than when walking without using a smart phone (p<0.05). The splenius capitis, lower trapezius, triceps, multifidus, and erector spinae increased muscle activity when walking while texting to the smartphone than when walking without using a smartphone (p>0.05). Second, when using a smartphone, the speed was slower than upright walking (p<0.05). Third, when using a smartphone, the bending angle of the neck increased more than when upright walking (p<0.05). Conclusion Our findings suggest that habitually using a smartphone while walking could be a potential risk for trunk musculoskeletal problems.