In this study, we demonstrate the use of orthogonal diffuse reflectance spectroscopy (o-DRS) to assess brain dysfunction and to monitor internal temperature variations during heatstroke in intact mice brains (n=6). Heatstroke is a medical emergency defined by abnormally elevated body temperature greater than 40°C that causes biochemical, physiological and hematological changes (multiorgan damage). Therefore, quick diagnosis and management of heatstroke victims is essential for good outcomes. Current clinical methods for monitoring temperature (invasive and noninvasive) suffers from several drawbacks such as complexity, cost, portability, safety, etc. To overcomes these deficiencies, a DRS working at the spectral range of 600-1000nm in orthogonal mode together with numerical processing have been applied to First, monitor cerebral optical changes, Second, evaluate rise in temperature and Third, to predict internal temperature noninvasively. Heatstroke was induced by exposing of the anesthetized mouse body, placed above controlled heating pad, to a high ambient temperature with increasing intervals of 1°C until death. Experimental results show variations in both absorption and scattering during heatstroke which emphasizes the changes in brain chromophores and morphology that occur during temperature elevation. In addition, a reflectance-temperature index was developed and found to correlate well with the measured temperature. Our preliminary results suggest that our o-DRS have the potential to monitor and assess internal temperature variations and thus may serve as a useful tool in clinical and laboratory settings.