This communication reports physiologic and structural characteristics of phage Z63-B2 active on Lactobacillus fermentum strain ATCC 9338; a comparison with phage Z63-B1, previously isolated from the same kind of environment (sourdoughs for bread-making) was discussed. Z63-B2 showed a multiplicative cycle with a burst size of 100 PFU per infectious centre and a latent period of 150 min. Its electrophoretical profile of proteins differed from that of phage Z63-B1 only for one minor protein. DNA fragments obtained with different Restriction enzymes resulted very similar and a high homology between the viruses was confirmed by hybridization tests. Two phages prove to be Variants each other. Resistant clones to phage Z63-B2 isolated after lysis of the host strain, showed costantly a different cell morphology and colony growth in comparison with the original host strain; however resistance was not imputable to a lysogenic state.