Plasma irradiation on surface of heat-cured acrylic resin prior to processing self-curing acrylic resin is likely to effectively increase the adhesive strength between these materials for short-term period. However, long-term reliability of adhesive strength between these materials has not been clarified yet. In the present study, these materials were stored in water for a long period (100 days), and the effect on their shear bond strength was investigated. Forty-four test specimens with flat bonding test surface were made with heat-cured acrylic resin. They were divided into four groups according to treatment procedures for bonding surface: plasma treatment, adhesive primer application, adhesive primer application after plasma treatment, and no treatment (for control). Self-curing acrylic resin was processed against all bonding surfaces. After storage in water for 100 days, shear bond strength values between heat-cured and self-cured acrylic resins were measured. Specimens in plasma treatment group exhibited higher shear bond strength value than those in control, although the difference was not significant.