The possibility of using attenuated total reflectance terahertz (ATR-THz) spectroscopy which is a new technic for measuring somatic cell count (SCC) was investigated. Milk samples controlled SCC derived from non-homogenized raw milk were prepared. The spectral signals of samples in the terahertz region 40 - 400 cm-1 were measured by Fourier-Transform terahertz spectrometer. The ATR-THz spectroscopy was sensitive to SCC enough to discriminate from water information. As the model experiment, it was confirmed the penetration depth of ATR in our system was deep enough to measure large SCC in clinical mastitis milk. It was inferred that 2.3×107 cells cm-2 could be determined. This technic will be applied for a device which will offer the opportunity to conduct inline non-destructive measurements for detecting mastitis. Copyright © 2013 IFAC.