Dentist, dental technician and assistants are faced a several kinds of microorganisms during wor like bacteria, fungi and viruses .So, we can prevent cross contamination by using either chemica or mechanical disinfection. The aim of the research was to measure the effect of different types of chemical disinfection on the hardness of two types of denture base resin, heat activated acry and nylon (flexible). A total number of 80 denture resin specimens (40 specimens from hea activated acrylic and 40 specimens from flexible resin) were prepared. Each type of specim was subdivided into 4 groups. Three groups were divided according to the type of dentur disinfectants (1%sodium hypochlorite, 1% povidine/iodine, Kin solution) and the fourth whi considered as control group was immersed in distilled water. All specimens were immersed testing solution for 90 minutes at 370C. The hardness of the specimens before and af immersion was tested using Shore D machine. Our study showed that the mean value hardness test for poly methyl methacrylate higher than polyamide and there need aid non significant Contrast in the resistance of the surface to scratches and indentation between diver sorts of thermoplastic resin after using chemical disinfectant and denture cleansers w i comparison with control group for each type of denture base resin. The resistance to indentati of different types of denture base would not affected by short time immersion in chemica disinfectant.