High intensity focused ultrasound (HIFU) is a noninvasive technique that has great potential for improving thermal therapies. To target specified regions accurately for treatment, a robust imaging technique is required to monitor HIFU application. Therefore, the development of an ultrasonic imaging technique for monitoring HIFU treatment is highly medically significant. Quantitative ultrasound (QUS) is a novel imaging technique that may improve monitoring of HIFU treatment by quantifying tissue changes. Ultrasonic backscatter experiments were performed on two types of phantoms to understand the variations in QUS parameters with increases in temperature from 36 to 50°C. The phantoms were biological phantoms made of agar and containing either mouse mammary carcinoma cells (4T1) or chinese hamster ovary cells (CHO) as scatterers. All scatterers were uniformly distributed spatially at random throughout the phantoms. Sound speed and attenuation were estimated in the phantoms versus temperature using insertion loss methods. Two parameters were estimated from the backscatter coefficient (effective scatterer diameter (ESD) and effective acoustic concentration (EAC)) and two parameters were estimated from the envelope statistics (κ parameter and μ parameter) of the backscattered echoes versus temperature. The results of this study suggest that QUS has the potential to be used for noninvasive monitoring of temperature changes in tissues.