Survival of biocontrol agents and their effective colonization of rhizhosphere are the essential components for successful disease suppression. The effects of hydrogel supplement on bacterial survival and disease control were evaluated in pot and in the field. Addition of 2% hydrogel material to potting soil resulted in significant enhancement of colonization of biocontrol agent Serratia plymuthica A21-4 both in soil and rhizosphere of pepper plants. Rhizosphere colonization of S. plymuthica A21-4 retrieved from 40 days old pepper seedlings indicated 100 times higher bacterial population in hydrogel treated soil than in ordinary pot soil. The pepper plants sown in hydrogelated potting soil showed higher seed germination rate and the better growth of pepper plant than those in ordinary commercial pot soil. Although the suppression of Phytophthora capsici density in the potting soil by treatment of biocontrol agent A21-4 was not significantly different between in hydrogelated soil and ordinary potting soil, the suppression of Phytophthora blight between two treatments was significantly different. A21-4 treatment in hydrogelated potting soil was completely disease-free while same treatment in ordinary potting soil revealed 36% disease incidence. Our field study under natural disease occurrence also showed significantly less disease incidence (12.3%) in the A21-4 treatment in the hydrogelated soil compared to other treatments. Yield promotion of pepper by the A21-4 treatment in the hydrogelated potting soil was also recognized. Our results indicated that hydrogel amendment with biocontrol agent in pot soil would be a good alternative to protect pepper seedlings and increase plant yield.