Objectives: The present study aimed to comparatively evaluate the influence of oral rinse solutions and tooth brushing on stainability of thermoplastic tooth colored prosthetic materials, using computerized spectrophotometry before and after immersion. Materials and Methods: Fifty-six samples (Twenty-eight samples of each material); Acetal resin and polyether ether keton(PEEK) were constructed in the form of discs (10 mm in diameter and 2 mm in thickness). Samples were randomly divided into 4 subgroups (n=7) according to the oral rise solutions (chlorhexidine, benzydamine HCl, alcohol-free mouthwash) and artificial saliva as control. Simulated tooth brushing of samples for 4 min with rotary instruments was applied before immersion in mouth rinses. The mean of color values (L*,a*,b*) of each specimen were measured before and one week after exposure with a Reflective spectrophotometer. Results: regardless to staining solutions totally it was shown that Acetal resin material group recorded higher color change mean value (4.75±0.52 ΔE) than PEEK material group mean value (4.64±0.66 ΔE).The difference between both materials groups means values was statistically non-significant as indicated by two-way ANOVA (F=0.31, P=0.5748>0.05). On the other hand Listerine zero recorded the highest color change mean value (5.05±0.5 ΔE) followed by Tantum V solution mean value (4.91±0.37ΔE) then CHX solution mean value (4.52±0.7 ΔE) while A. saliva solution recorded the lowest color change mean value (4.29±0.52 ΔE). Conclusions:1- There was a highly significant difference between alcohol free, benzydamine HCL & CHX mouth rinses. The listerine zero showed the highest value in staining potential while CHX was the lowest regarding acetal 2- Among the two thermoplastic restorative materials and although statisticaly non significant, PEEK was found to be the higher color stable material and the higher stain was taken up by acetal resin. 3- There were no significant differences between the discoloration effects of different mouth washes used in this study on PEEK material.