A sensitive high performance liquid chromatography tandem mass spectrometric (HPLC MS/MS) method has been developed for simultaneous determination of nine antibiotics residues (oxytetracycline,tetracycline,chlortetracycline,doxycycline,penicillin G,procaine penicillin,sulfadiazine,sulfadimidine and sulfathiazole) in organic fertilizer.It is of great significance to the rapid detection of antibiotic residues in organic fertilizers.In this paper,the samples were extracted by ultrasonic oscillation with Na2EDTA McIlvaine buffer solution,then extracts was cleaned up by the Strata SDB L solid phase extraction column.The contents of antibiotics were determined by high performance liquid chromatography tandem mass spectrometry and calculated by external standard method.Multiple reactions monitoring mode was utilized.Most analytes were scanned by positive ion electrospray ionization except penicillin G.Average recoveries of the nine analytes were in the range of 631% to 934% at spiking levels of 0.1,0.5 and 1.0 mg/kg.Relative standard deviations were between 1.7% and 9.5%.The method detection limits of tetracycline antibiotics were 0.05 mg/kg,and the method detection limits of sulfonamides and penicillins were 0.02 mg/kg.The method was convenient,fast,with good reproducibility,and could be used to simultaneously and fast confirm multi residue of antibiotics in organic fertilizer.