Abstract: Dynamic changes of proteins in in-vitro cultures of Fisher navel over periodical sub-culturings were analyzed with SDS-Polyacrylamide gel electrophoresis. Results showed that the quantity of total expression proteins in the early in-vitro cultures were lower than that in field plant, however, it increased and trended to stability in the later in-vitro cultures of Fisher navel. The expression quantity of 21 and 31 KDa proteins were increased when sub-cultured for the second cycles, and the former protein was expressed specifically in citrus. The protein of 21 KDa was also identified by mass spectrum after it was purified by modified electric elution method aided with dialysis tube. Results indicated that the sequence similarity of this protein compared with all that of proteins published in database was lower than 50%. It was suggested that this protein was a novel protein with no information about its functions, so that much work remains for realizing the effect of the protein on in-vitro culture of Fisher navel in the process of sub-culturings.