Three bacterial isolates (69B1, KM and AE) were used in this study, they were characterized according to (Shirling and Gottlieb 1966) as Streptomyces spp. These isolates have, antimicrobial activities against. Gram positive bacteria, but not against Gram negative, and resist higher concentrations of erythromycin; Therefore, such isolates may considered to be as possible produces of macrolide-like antibiotics. Antimicrobial activities of the three isolates were detected in the solid and liquid media. On solid medium, antibiotic synthesis started before aerial mycelia formation and increased continuously till the formation of aerial mycelia, then the levels of antibiotic(s) produced in culture media remain constant. On the other hand, antibiotic synthesis started in the liquid medium when mycelial growth ceased. The obtained results showed that, antibiotic synthesis by EM and AE isolates on the solid medium was greater than that in the liquid medium, while antibiotic synthesis by 69B1 isolates was the same in both solid and liquid media. Variants of 69BI EM and AE isolates, which resisted higher concentrations of erythrormycin were assayed for antibiotic production and resistance to various antibiotics. KM and AK variants produced same amounts of antibiotics as compared with parental isolates, however, their produced larger amount of the antibiotic with increasing resistance to erythromycin its sensitivity for various antibiotics decreased. TLC procedure for detection of macrolide antibiotics, showed two spots in 69B1 and single spot in EM and AE with R values close to Spot of standard eryhtromycin. Curing experiment using acridine orange indicated that plasmid DNA of EM isolate has a role in antibiotic synthesis, melanin production and sporulation. Single plasmid band was detected in the original isolate this band could not be detected in curd colonies.