The purpose of this study was to investigate the physical effect of tissue conditioner on polymerized acrylic resins. Surface hardness and transverse strength were measured for evaluating physical effect of tissue conditioner on polymerized acrylic resins. 1) To measured surface hardness, the resin specimens($65{ imes}10{ imes}10mm$ size) of each resin material were made, applied tissue conditioner, stored in $37^{circ}C$ water for 1 week, and changed tissue conditioner every week for 3 weeks. Surface hardness was measured every week with Shore hardness tester for 4 weeks. 2) To measured transverse strength, the resin specimens($65{ imes}10{ imes}3mm$ size & $65{ imes}10{ imes}1.5mm$) of each resin material were made. The specimens were divided into four groups, and measured by universial testing machine. Group I(control group) : The resin specimens were stored in $37^{circ}C$ water for 5 weeks. Group II : The resin specimens were stored in $37^{circ}C$ water for 5 weeks, and relined in 1.5mm thickness with same resin. Group III : The resin specimens were stored in $37^{circ}C$ water for 1 week, applied tissue conditioner in 1.5mm thickness, stored in $37^{circ}C$ water for 1 week, changed tissue conditioner and water every week for 3 weeks, removed tissue conditioner, reduced 1.5mm thickness from resin surface which was applied tissue conditioner, and relined in 1.5mm thickness with same resin. The following conclusions were obtained : 1. Surface hardness changes of Vertex RS and Vertex SC were not different significantly(p>0.01). 2. Surface hardness of K-33, Tokuso rebase, and Kooliner were decreased(p<0.01). 3. With the exception of Kooliner, transverse strength of all resin materials between control group and groups which applied with tissue conditioner were not different significantly(p>0.01).