Concurrent use of a smartphone while walking may influence low back muscle activation patterns due to restricted arm motions, limited trunk rotation and walking with the head in a flexed position. The objective of this study was to quantitatively determine the effects of smartphone use while walking on the level of myoelectric activity of the low back extensor muscles. Fifteen asymptomatic young smartphone users who were familiar with smartphone use while walking participated in this experiment. The electromyography (EMG) of the lumbar erector spinae muscles were collected bilaterally when they were conducting three walking tasks on a treadmill: 1) walking without smartphone use (upright walking); 2) web-browsing while walking; and, 3) texting while walking. Results found that the normalized EMG of the lumbar erector spinae muscles were significantly (p<0.05) greater when using a smartphone while walking as compared to when walking without using the phone. It indicates that using a smartphone while walking could pose larger muscular load to the low back extensor muscles than that of walking without using a phone.