- In this paper, the optical properties of benign and malignant human brain tumors has been investigated to provide a new optical diagnosis method. The nonlinear behavior of all samples has been studied using Z-scan technique and also, their optical density (optical absorbance) by a simple optical setup. The obtained experimental results show that optical density for malignant is more than benign tissues and also, nonlinear behavior of benign and malignant tissues is completely different. Obviously, the nonlinear refractive index appears for benign tumor with negative sign and for malignant tumor with positive sign. In summary, this study shows that Z-scan technique can be used for early diagnosis of malignant brain tissue from benign.