Abstract.[Purpose] The purpose of this study was to identify the effects of longus colli muscle massage on the cervical extension range of motion of adults.[Subjects] A total of 60 subjects were divided into two different group; 30 were assigned to the experimental group, and the other 30 to the control group.[Methods] The experimental group received massage of the longus colli muscle, which is a deep neck flexor, whereas the control group received massage of the superficial neck muscles. The experimental and control groups were both measured for cervical flexion, extension, left rotation, right rotation, left lateral flexion, and right lateral flexion range of motion (ROM).[Results] The measurements after the experiment showed the experimental group had a statistically significant increase in all the directions. Meanwhile, the control group exhibited a statistically significant increase in all directions except for rotation to the left. For the two groups, independent sample t-tests before the experiment, after the experiment, and on the differences between the pre-test and post-test values showed a statistically significant difference only in cervical extension. [Conclusion] This experiment demonstrated that massage of the longus colli muscle, known as a deep neck flexor, were more effective than massages of superficial neck muscles. Based on this result, we recommend longus colli massage in clinical practice in for enhancing patients' cervical extension ROM.