Abstract:The effect of phosphate buffer on protective enzyme system was different as the way of treatment and wheat (Triticum aestivum L. ) species. Normally superoxide dismutase (SOD) and peroxidase (POD) activity increased markedly. The former decreased with the increase of SO2 fumigation dosage but it was higher than control and producted new isoenzyme pedigree. The latter increased according to SO2 fumigation and showed relative gain effect with phosphate buffer the isoenzyme pedigree increased markedly. The change of protective enzyme system of scavenging free radicals was possible one cause that phosphate buffer eased SO2 insult of wheat seedlings.