Abstract: In order to use Pythium oligandrum，develop safe，nontoxic and high-efficient biological agent and control Phytophthora disease in pepper cultivation. P. oligandrum CQ2010，a self-isolated biocontrol strain，was used to produce biological agent（P. oligandrum agent，POA）and then the effects of POA on Phytophthora disease control and growth-promotion were investigated through culture，antagonism，and field experiments. P. oligandrum CQ2010 secreted cellulase，protease，β-1,3-glucanase and chitinase. The hydrolysis circle diameters of the former three enzima were about or over than colonies on solid culture media. The extract of POA significantly inhibited the mycelial growth of Phytophthora capsici and the inhibitory rate was higher than metalaxyl Mancozeb and lower than Mandipropamid. In field experiment，the addition of POA into the soil around the roots of pepper seedlings significantly decreased the disease incidence and index of Phytophthora disease. POA showed a better preventive effect than the curative，which were 89.37% and 61.19%，respectively. Pepper plants applied POA bloomed and fruited 6–9 days earlier than the control（without POA）. In addition，POA application increased plant biomass by 32.03%，nutrient absorption by 35.74%（N），40.53%（P）and 53.23%（K），and fruit yield by 25.21%. Concomitantly, fruit quality was improved due to higher soluble proteins, free amino acids, soluble sugars，and vitamin C but similar content of nitrate compared to the control. P. oligandrum CQ2010 effused enzymes that hydrolyze the cell walls of pathogenic fungi. The extract of POA inhibited the mycelial growth of Phytophthora capsici. POA application decreased the disease incidence and index of pepper Phytophthora，promoted plant growth and development，increased fruit yields，and improved fruit quality. Therefore，POA has a broad application prospect and will be suitable for mass production.

Key words: Pythium oligandrum, Phytophthora capsici, growth promoting, biological control