Fire blight, caused by Erwinia amylovora is the most destructive disease on pear in Egypt. In this study water, ethanol, and chloroform extracts of eighteen medicinal plants were tested against Erwinia amylovora. Obtained results showed that garlic, harmel, madder, thyme and garden sage extracts were effective in inhibiting the growth of E. amylovora in vitro, while madder, harmel and thyme extracts were the most effective in vivo trials. Also, in this study the effect of some extracts, i.e., madder, garlic, thyme, harmel and garden sage, were tested in inhibiting the growth of seven isolates of E. amylovora resistant to streptomycin sulfate and the result showed that garlic, madder and harmel were more suppressive to some isolates than the sensitive. Active ingredients of harmel, thyme and garlic extracts were separated and tested for their effect on inhibiting growth of the fire blight pathogen. With respect to cellular protein pattern, the results revealed that some proteins were present in all resistant and sensitive isolates either treated with madder extract or extract-free. However, they were absent in the same isolates treated with harmel extract. Also, harmel extract inhibited the synthesis of some proteins that have low molecular weight in either resistant or sensitive isolates. Madder extract activates the production of a protein in streptomycin sensitive isolates and suppress the synthesis of other proteins in the same isolates. However, madder extract has inhibited the production of same low molecular weight protein in streptomycin resistant isolates.