The present invention relates to a novel and economical process for modification of acid scavenger to be used not only for neutralizing the effect of catalyst residue but as well as crystallinity modifier in polyolefins. More particularly, the present invention discloses a process for modification of acid scavenger to be used as dual functional additive as acid scavenger as well as crystallinity modifier in polyolefins, said process comprising treating an acid scavenger with an organic dibasic acid to obtain a modified acid scavenger, wherein the acid scavenger is calcium aluminum hydroxy carbonate having chemical formula Ca4Al2(OH)12CO3.nH2O, where n=4-5.