Statement of problem: The microbial adhesion on the surface of materials used in prosthodontics and restorative dentistry significantly influences microbial infection. Purpose: The purpose of this study was to evaluate the effect of how the degree of surface roughness of acrlyic resin affect the adhesion of bacteria. Material and methods: Resins were finished with $50{mu}m$ and $250{mu}m$ aluminium oxide particles by using sandblaster, by using stone point, and high polished with $Opa^{(R)}$ and Lace $motor^{(R)}$. The surface of acrylic resin attached by bacteria was directly touched on the surface of BHI agar, which was incubated. Bacteria colonies formed on BHI agar were counted in accordance with the degree of the surface roughness. Results: 1. The viable cell number of Streptococcus mutans increased on the acrylic resins incubated in BHI broth than in PBS. 2. The viable cell number of Streptococcus mutans increased on the acrylic resins incubated without agitation than with agitation, washed three times than six times, and incubated in broth added with 5% sucrose than without sucrose. 3. When Streptococcus mutans incubated in BHI broth, the number of Streptococcus mutans colonies formed on BHI agar was the largest on the acrylic resins finished with $250{mu}m$ aluminium oxide particle using sandblaster. But when incubated in BHI broth containing sucrose, the number of colonies formed on that was the largest on the acrylic resins high polished using $Opal^{(R)}$ and Lace $motor^{(R)}$. 4. When Streptococcus sanguis was incubated in BHI broth with or without sucrose, the number of Streptococcus mutans colonies formed on BHI agar was the largest on the acrylic resins finished with $250{mu}m$ aluminium oxide particle using sandblaster. 5. When Actinomyces viscosus was incubated in BHI broth with or without sucrose, the number of Streptococcus mutans colonies formed on BHI agar was the largest on the acrylic resins high polished using $Opal^{(R)}$ and Lace $motor^{(R)}$. Conclusion: These results indicated that when acrylic resins attached by bacteria were touched on the surface of BHI agar, the number of bacterial colonies formed on the agar was dependent on the bacterial species. Also, the result of this study was showed that increase in the surface roughness and the addition of sucrose increased retention of microbial cells.