Aims: Evaluation of the surface hardness of heat-treated acrylic resin after modifying it with three different techniques. Materials and Methods: Heat cured acrylic resin was modified by: (a) The copolymerization of acrylic resin with 5% and 10% of acrylic acid (AA), (b) The addition of 5% and 10% thermally activated zinc oxide (ZnO) and (c) The chemical bonding or engagement of Zinc ions into the polymer chain by an organic link, zinc diacrylate (ZDA) in 5% and 10%, to get a copolymer. The acrylic specimens have dimensions of (30, 15 and 3) ± 0.2 mm. Surface hardness was determined using a Durometer (Shore D) hardness tester. Results: There was general increase of the surface hardness of the experimental (modified) groups. A statical significant increase in the hardness of both acrylic groups modified by 10% ZnO and 10% ZDA compared to the control group and the remaining modified samples. Conclusion: Two techniques had significantly improved the hardness of heat cured acrylic resin; either by adding 10% by weight of thermally activated ZnO or by copolymerizing it with 10% by weight of ZDA to get poly (methyl methacrylate -co-zinc acrylate) copolymer.