A process for preparation of (2S,5R)-7-oxo-6-sulphooxy-2-[((3R)-pyrrolidine-3-carbonyl)-hydrazino carbonyl]-1,6-diaza-bicyclo[3.2.1]octane is disclosed comprising reacting a compound of Formula (II) with a compound of Formula (III) to obtain a compound of Formula (IV). The crystalline end-product is als claimed.