An improved method for manufacture of simvastatin of formula (I) in high purity. The process for preparation of compound (I) comprises the steps of agitating a compound of formula (II), wherein R is hydrogen, NH4+ or an alkali metal in an organic solvent and in an inert atmosphere at a temperature of between 27° C. to 40° C. in the presence of a weak acid followed by neutralization with an organic base and obtaining compound of formula (I) in high purity and substantially free of impurities through a step of isolation and crystallization.