Background: Studying and investigating the transverse strength(Ts), impact strength(Is), hardness (Hr) and surfaceroughness(Ra) of conventional and modified autopolymerizing acrylic resin with different weight percentages ofbiopolymer kraftlignin, after curing in different water temperatures; 40°C and 80°C.Material and Methods: Standard acrylic specimens were fabricated according to ADA specification No.12 fortransverse strength, ISO 179 was used for impact testing, Shore D for hardness and profilometerfor surface roughness.The material lignin first dispersed in the monomer, then the powder PMMA is immediately added. Lignin added indifferent weight percentages. Then cured using pressure pot (Ivomet) in two temperatures;40°C and 80°C under 2bar pressure, for 30 minutes.Atotal of 144samples were prepared for this study. Ts, Is, Ra, and Hr were tested, by usingInstron universal testing machine, charpy impact tester, shore D tester, and profilometer respectively.Results: The transverse strength increased in both the conventional and modified onewhen compared with thatcured in air. The addition of 0.5wt% lignin gave the higher effect (78.0017MPa) with highly significant difference foundbetween groups at 40°C polymerizing temperature. While the impact strength in both temperatures in the modifiedresin revealed increased results than conventional one, 1.25wt% of kraft lignin gave the highest value (12.7355KJ/m2)with highly significant differences found between groups at 80°C polymerizing temperature. Hardness and surfaceroughness showed also highly significant differences found between groups at 40°C polymerizing temperature, allthe groups had increased Hr. than the control one (78.95), while the Ra. decreased for 1.0% ,1.25,1.50 and 1.75 wt%lignin content to (0.26,0.10,0.063, 0.12μm) respectively in 40°C polymerizing temperature, the lowest value present in1.75 wt% lignin (0.05 μm) at 80°Cpolymerizing temperature.Conclusions: It seems that increasing the polymerizing temperature to 40°C had a positive effect on the mechanicalproperties of autopolymerizing acrylic resin and the one enforced by kraft lignin biopolymer in low percentages.Increasing the polymerizing temperature to 80°C will doesn’t have much positive effect but it doesn’t deteriorate themechanical properties. However, when submitted to increasing the temperature to 80°C, specimens showed asignificantincrease in impact strength.