Objective: To optimize the microwave-assisted extraction process of Rosa roxbunghii Tratt polysaccharide (RRTP) from the Rosa roxbunghii Tratt (RRT) dried fruit and evaluate the antitumor activities of RRTP extracted by the optimum processing conditions. Methods: Taking the yield of polysaccharides as the index, and based on the single factor test, the extraction process parameters were optimized by the response surface experiment to establish the model of S₁₈₀ solid tumor to study the antitumor activities of RRTP. Results: The optimum extraction conditions for RRTP were as follows: microwave power 240 W, liquid to solid 37∶1 （mL/g）, microwave time 24 min, 3 times of microwave extraction. The yield of RRTP was (3.19±0.05)% on average under the optimum processing conditions. Besides, antitumor activity analysis showed that RRTP had obvious antitumor activity and could significantly increase leukocyte count, thymus index and spleen index in S₁₈₀ solid tumor mice. It was indicated that RRTP had a tumor inhibitory rate of (52.13±1.84)% in S₁₈₀ solid tumor mice, which was stronger than ultrasound-assisted extraction of RRTP at the same gastric irrigation dose at 100 mg/kg. Conclusion: The RRTP extracted by optimum microwave-assisted processing conditions can improve the immune ability and antitumor activity of S₁₈₀ solid tumor mice and could be used as a potential functional food supplements.