Objectives: This study aimed to compare the amount of deep tissue pressure and muscle relaxation between a soft inflatable rubber ball (SIRES) and a hard massage ball (HMB). Design: Crossover experimental design study. Interventions: Thirty participants with neck pain (age: 65.9 +/- 3.4, Neck Disability Index score: 34.0% +/- 15.2) pillowed a SIRS or an HMB beneath the suboccipital region in the supine position. For the baseline condition, participants pillowed a foam block without a ball. Main outcome measures: To quantify the amount of deep-tissue pressure by a ball, compressed soft tissue thickness was measured with lateral cervical radiographs. To assess muscle relaxation, the amount of muscle tension was determined using electromyography of the sternocleidomastoid and upper trapezius muscles. To monitor the cervical lordosis in each condition, the extension angles of the cervical vertebrae were quantified using the relative rotation angles. Results: The compressed soft tissue thickness in the SIRB condition was significantly lower than that in the HMB condition. The normalised muscle activities exhibited that right sternocleidomastoid muscle activity in the HMB condition was significantly higher than that in the baseline and SIRS conditions. In the SIRB and HMB conditions, Numeric Rating Scale for pain was 0.2 +/- 0.5 and 5.2 +/- 1.4, respectively. Conclusions: Our findings demonstrate that a SIRB is more advantageous than an HMB for pressing the soft tissue deeply. This finding would be related to reduced muscle tension and discomfort in the SIRS condition when compared with the HMB condition.