The objective of this study was to quantify head flexion when using a smartphone while walking. Head flexion angle in the sagittal plane was measured from twenty-eight young users when conducting one-handed web-browsing while walking, two-handed texting while walking, and walking upright on a 60-m walkway. Participants walked with the head flexed 38.5° (median angle) during the two-handed texting and it was significantly greater (p < 0.05) than that of the one-handed web-browsing (31.1°) as well as of upright walking (−1.2°). The study results indicated that using a smartphone while walking would pose a larger load to the neck musculature compared to when walking without using a phone, and the load would be greater for two-handed texting than for one-handed browsing among the two smartphone tasks. The findings of this study can be used to inform smartphone users of potential risks of smartphone use while walking.