The mimosine contents of Leucaena foliage, Acacia tannins and total phenols from leaf, bark and pod were analyzed by a near infrared reflectance spectrophotometer (Compscan 3000). A calibration equation (linear summation regression) was developed with near infrared spectral analysis software, using 30 spectra from old and young leaves of Leucaena and 23 spectra from different samples of Acacia. Each constituent required four wavelengths, i.e. Leucaena mimosine 1901, 2071, 2227 and 2234 nm; Acacia total phenols 1914, 2066, 2179 and 2183 nm; and tannins 2152, 2178, 2183 and 2295 nm, to derive the best calibration equation with first derivative instrument maths (segment 5 and gap 15). The near infrared analyzer calculated that the percentages of mimosine. total phenols and tannins are closely comparable to laboratory results.