Hydroxynitrile lyase (HNL) from seeds of Prunus pseudoarmeniaca was partially purified by (NH(4))(2)SO(4) fractionation and covalently immobilized onto Eupergit C and Eupergit C 250 L The percentages of bound protein per gram of Eupergit C and Eupergit C 250 L were about 81 and 98 of the initial amount of protein, respectively. K(m) and V(max) values were determined 2.23 mM and 0.54 U/mg prot. for the free HNL, 1.60 m M and 0.87 U/mg prot. for the immobilized HNL onto Eupergit C and 1.03 mM and 0.35 U/mg prot. for the immobilized HNL onto Eupergit C 250 L respectively at optimized reaction conditions. The half lives (t(1/2)) and the thermal inactivation rate constants (k(i)) of free and immobilized HNLs were determined at 25 and 50 degrees C, immobilized HNLs displayed higher thermal stability. Carboligation activities of free and immobilized HNLs for (R)-mandelonitrile (R-MN) synthesis were also determined. Besides, reusabilities of immobilized HNLs for both lyase and carboligation activities were investigated by using batch type reactors. (C) 2010 Elsevier B.V. All rights reserved.