A double integrating spheres system for measuring the optical properties of tissue was designed. The optical properties have been measured (at 632.8 nm) when human whole blood and albumen were slowly heated in water bath at room temperature (23 ℃) and 37 ℃～80 ℃ for 15 minutes. There were different changes in optical properties when albumen and whole blood underwent denaturation and conformation changes. It was the reason that there were differet components between the two samples. It is demonstrated that physiological characteristic is described by optical properties of tissue. Optical detecting will provide a new method to monitor thermaltherapy.