Recombinant Hepatitis B core antigen (HBcAg) expressed in Escherichia coli, exhibits similar morphology and antigenicity to the native core particles of Hepatitis B virus (HBV). Also core particle has become one of the most frequently studied systems, as a carrier for various foreign epitopes. This aspect leads to great interest of HBcAg as a component for discovery of new type HBV vaccine, as therapeutic and diagnostic tool. Also core particles are examined as vectors for gene engineering. In this study there were investigated factors that influence the expression of HBcAg in Escherichia coli host RB791 under the transcriptional control of the lac promoter, and the conditions for maximizing biomass and HBcAg production rates of this system were discussed. Fermentation screening process in shaker flask state conditions was performed to specifically determinate the influence of IPTG (isopropyl-/3-o-thiogalactoside) or lactose concentration, temperature, composition of the growth medium, the time point in the growth profile at which the cells are induced with either IPTG or lactose, and the duration of the induction phase. Culture fermentations in laboratory scale bioreactor (working volume 2 L), were performed in three phases: biomass growth in batch and fed batch phases, and the product development in induction phase. Accordingly, the fed batch and induction phases were maintained by automatic addition of feeding solutions containing glucose, salts and microelements, and with inducer in induction phase. In this way the biomass growth was modelled, which was predicted on the basis of physiology and nutritional requirements of E. coli.