Rabbit liver cytosolic glutathione-s-transferase (GSTs; EC: 184.108.40.206) was immobilized in cross-linked gelatin cylindrical molds which the formaldehyde was used as cross linker. Glutathione-s-transferases are the enzymes that catalyze the conjugation of wide variety of electrophilic substrates with glutathione. This process generally leads to the detoxification of the xenobiotics. Characterization of immobilized GST was made by using 1-chloro-2,4-dinitrobenzene(CDNB) as substrate. Immobilization efficiency of the enzyme was calculated in terms of activity yield. Optimal enzyme, gelatin and formaldehyde amounts, optimum pH and temperature, Km[CDNB], Km[GSH] and thermal stability was searched and compared with the free enzyme. Furthermore, for studying the detoxification by conjugation in vitro, immobilized GST was tested using stirred batch reactor system and found suitable with a high yield of 2,4-dinitrophenyl-GSH conjugate formation.