The disclosure relates to a solid R-(+)-Iansoprazole butylamine salt and a process for preparing a stable R-(+)-Iansoprazole butylamine salt, wherein the process comprises the steps of:optically resolving racemic lansoprazole, isolating R-(+)- lansoprazole, and reacting the isolated R-(+)-Iansoprazole with a butylamine to form a stable R-(+)lansoprazole butylamine salt； (a) treating racemic lansoprazole with R-(+)-2,2'-dihydroxy-I,I'- binaphthyl ("R-(+)BINOL") in a suitable solvent to form the inclusion complex of R-(+)lansoprazole with R-(+)-BINOL；(b) removing the inclusion complex of R-(+)-Iansoprazole with R-(+)- BINOL prepared in step (a) from the solvent and adding a mixture of organic solvents； (c) crystallizing the R-(+)-Iansoprazole - R-(+)-BINOL inclusion complex from the mixture of organic solvents； (d) enriching the R-(+)-Iansoprazole - R-(+)-BINOL inclusion complex to obtain a purity of more than about 97% e.e.； (f) cleaving the enriched R-(+)-Iansoprazole - R-(+)BINOL inclusion complex； (g) separating the R-BINOL and R-(+)-Iansoprazole； (h) isolating the R-(+)-Iansoprazole； and (i) reacting the R-(+)-Iansoprazole with a butylamine to form a stable R-(+)lansoprazole butylamine salt.
