Abstract: In order to obtain an effective antagonistic microorganism against tobacco black shank(Phytophthora parasitica var.nicotianae),a Penicillium stain QMYCS-2 was isolated by the spread plate method from rhizosphere soil of healthy tobacco plants.This strain was identified to be Penicillium madriti based on its morphological characteristics and ITS-rDNA sequence analysis.The results of confronting culture between QMYCS-2 and P.parasitica var.nicotianae showed that:1) The inhibition rate of QMYCS-2 against the growth of P.parasitica var.nicotianae reached 71.76%.QMYCS-2 was cultured in five mediums for the fungi of plant pathogen,the inhibition effects of the obtained fermentation filtrate on P.parasitica var.nicotianae were determined.The result indicated that potato glucose liquid medium was the best culture medium.2) The inhibition effects of QMYCS-2 fermentation filtrate and penicillin on the growth of P.nicotianae var.nicotianae were compared,the inhibition rate of the former was 64.89%-100.00%,while the highest of the latter was 7.33%.The control efficiency of QMYCS-2 fermentation filtrate against tobacco black shank in greenhouse was 73.25%,which was close to that of metalaxyl mancozeb(71.50%),a conventional fungicide used to control black shank in tobacco production.