The aim of this research is to develop a mathematical model to describe the production of human antibody fragments of small sizernas ScFv, Fab, F(ab’), through fermentation of Escherichia coli BW25113 (ara). Th e fermentations are conducted in a fermenterrn(Chemap Ag) with a mechanical agitation. Th e entire phase of fermentation is monitored on-line using a data acquisition systemrnMFCS/WIN. A kinetic and stochiometric models are developed. Th e stochiometric model describes the biological process of biomassrngrowth. Th e kinetic analysis of experimental data about fermentation of E. coli is carried out for batch and fed-batch phase for thernproduction process. Th e batch analysis is described by material balances of substrate and biomass with Monod and Pirt equations.rnTh e fed-batch phase is modeled using the material balances on biomass, substrate and product and analyzing the variation on volumernduring the time. Runge and Kutta algorithm is used to resolve the system equations. Result show that the equation that describernthe growth of biomass is: C6H12O6+3.56O2+0.52ONH3→2.13CH1,92O0,3N0,24+3,87CO2+4,74H2O. For the Monod and Pirt law thernfollowing parameters are found by regression of experimental data during the batch phase: μmax is 0.55 h-1, Ks is 0.10 g/L, Yx/s isrn0.35. Th e kinetics parameters that describe the fed-batch phase are the following: μmax is 0.24 h-1, Ks is 1.5 g/L, Yx/s is 0.34, m isrn0.02, α is 0.00043, β is 0.00007, Yp/s is 0.00084. A sensitivity analysis is carried out to verify the effi ciency of the mathematical model,rnvarying the values of parameters about ±10%: Evident variations are not present so the model is robust and stable. Th e realizedrnmathematical models can be used to optimize the pilot plant and for the planning of the laboratory tests.