Abstract: The objective of this study is to explore a new method for noninvasive temperature estimation of microwave hyperthermia using ultrasonic integrated backscatter(IBS). Water bath heating experiments were performed to fresh in vitro porcine liver tissues,and original ultrasonic radiofrequency signals at different temperatures were collected. IBS at each temperature was analyzed,and the correlation model between IBS and temperature was built for temperature estimation in microwave heating experiments. The correlation model was: IBS = 0. 062 × t + 3.591. The correlation model based temperature estimation for microwave hyperthermia had a small error(< 5 ℃) in the temperature range ≤70 ℃,and a larger error(>10 ℃) in the temperature range >70 ℃. Experimental results indicate that: 1) IBS may be used for noninvasive temperature estimation of mild hyperthermia; 2) because of the heterogeneity of temperature distribution in microwave hyperthermia,it was difficult to estimate the temperature accurately; and 3) it may be a potential approach for detecting thermal coagulation zones based on the difference between the IBS of normal and coagulated tissues.