Cephalosporium maydis the causal organism of late wilt disease of maize is still considered one of the most important fungal diseases in the Egyptian corn fields. The fungus was internally and externally seed- borne in white and yellow cultivars (Michail et al., 1999). Cephalosporins are  products of the genus Cephalosporium. Such products are regarded as a group of B-lactam drugs has antimicrobial effect. Bioassay studies of Cephalosporin-C produced by C. maydis isolates as well as pure Cephalosporin-C and four semi-senthytic derivatives (Cephalexin, Cefatrexyl, Claforan, Curisafe) were carried out against many bacterial and fungal isolates . According to the aformentioned results, the antibacterial spectrum of such antibiotics was mainly specific to certain bacteria. Claforan (Cefotaxime sodium) showed the highest inhibitory effect of bacterial growth, especially the tested strains of Erwinia amylovora, (sensitive and resistant strains of streptomycin) and Erwinia chrysanthemi pathovar. zeae (Syn. E. carotovora var. zeae) the corn stalk rot incitant  at the rate of 2mg/ml. On the otherhand, all the used Cephalosporins products haven't any antifungal effect on corn stalk or ear rot even on  the high dosage. Results also indicated that pure Cepanthalosporin-C and the same compound produced by C. maydis was less effective than other semi-synthetic derivatives of Cephalosporin-C.