[Purpose] To investigate the effects of core strength training on core stability with and without the Valsalva maneuver. [Participants and Methods] Twenty-four students were randomly assigned to the training and control groups. Students in the training group undertook a 4-week training program that included exercises for the transverse abdominis, multifidus, diaphragm, and pelvic floor muscles, whereas students in the control group performed their usual activities. Participants were required to perform four types of task with and without the Valsalva maneuver. Seated stabilometry was assessed according to the center of pressure (COP). [Results] In the training group, the rectus area in the quiet sitting position with the Valsalva maneuver was enlarged and the length of trajectory during a sudden perturbation task was decreased. No significant changes to the COP were seen in the control group. [Conclusion] Some parameters of core stability improved after participants completed a 4-week core strength training program.