Abstract: On purpose to examine the role of the weak positron irradiation in production of the chi-rality of biomolecules,the sublimed D-,L-and D,L- leucines are irradiated with 22Na source for 0,6,12,240 hours respectively and then the lifetime spectra of each isomer is continually detected twice. All the lifetime spectra are fit according to three components. The intensities of o-Ps in the sublimed isomers decrease in the order: L > D with an average ratio D/L =0. 87 but in the crystalline isomer the ratio lies between 0. 92 to 1. 02. These results coincide with Norden's experiment. The L isomers of leucine favour triplet states in case of forward polarized β particles. Mason suggested that the longitudinally polarized positrons,which have a parallel orientation of spin and direction of motion.may interact differently with D and L isomers of a chiral compound resulting in slight variances in the Ps formation probability and also in a change of the ratio of o-Ps to p-Ps formation. It is found that positrons interact differently with the isomers of leucine but o-Ps formed preferentially in the L isomers. On the basis of the consideration for the difference in helicity between β particles and positrons emitted from natural nuclides--β- particle has its spin opposite to its momentum(left-handed helicity),while positron with its spin parallel to its momentum (right-handed helicity). These experimental results show that asymmetrical interaction of positrons with O-,L-and D,L- leucine exists in primary state.