With pressed kBr disk technique the methyl-sulf amino-acid-the nutritious restrictive amino-acid of poultry was determined by internal standard-derivative infrared spectroscopy. The suitalbe internal standard-CaSO4 was selected, and peak height, peak area, first derivative and second derivative methods were used. In the determination,we selected undisturbed peak at 553 cm(-1) as standard. The correlation coefficient of standard curve equation were in the range of 0.993-0.998. The result was satisfied.