The Phospholipase A₂ superfamily is a broad and growing group of enzymes that catalyze the stereospecific cleavage of the sn-2 acyl ester union of diacyl-glycerophospholipids and liberate 1-acyl-2-lysophospholipids and free fatty acids. In plants, secretory PLA₂s (sPLA₂s) mediate a variety of cellular processes, including growth, defense and stress response. On the other hand, the enzymatically produced lysoderivatives are strong bioemulsifyers with numerous applications in food and pharmaceutical industries. The aim of the present work was to obtain a Phospholipase A₂ enzyme from soybean (Glycine max) and study its enzymatic properties. This is the first time a secretory Phosphalipase A₂ (sPLA₂) from soybean seeds, denoted as GmsPLA₂-I, was produced by heterologous expression in E.coli, renatured from inclusion bodies by guanidine treatment and purified by ion exchange chromatography. The cDNA encoded a mature protein of 114 amino acid residues with a signal peptide of 24 residues. The amino acid sequence for the mature GmsPLA₂-I contains 12 cysteines, the Ca^2+- binding loop (YGKYCGxxxxGC) and the active site motif (DACCxxHDxC), that are commonly conserved in sPLA₂s from plants. Phospholipase A₂ activity was evaluated by means of two techniques to obtain the optimum conditions for catalysis. First, mixed micelles of phospholipid/Triton X-100 were used in a titration assay in order to study the effect of pH and the Ca²⁺ ion on sPLA₂ activity and to determine the kinetic parameters (V_max and K_m). On the other hand, Langmuir-monolayer assays were performed in order to study the relation of the activity of GmPLA₂-I with the lateral surface pressure and the concentration, by using dilauroylphosphatidylcholine (DLPC) as a substrate. The Lag time as a function of DLPC-monolayer surface pressure and GmPLA₂-I concentration were determined.