This study deals with the hydrolytic step-growth polymerization Of E-caprolactam to produce nylon-6 in a semibatch reactor at near industrial conditions. e-caprolactam is polymerized in a 1.6 L stainless steel reactor at three different initial water concentrations, 4.43% (by mass), 2.52%, and 3.45%, respectively. During the polymerization, the values of the temperature and the pressure are controlled and recorded. Samples of the liquid reaction mass are taken from the reactor at different times and analyzed. The monomer conversions are obtained gravimetrically (in terms of water extractibles) as well as by using gas chromatography. The samples are also analyzed for the degree of polymerization using amide and acid end-group concentrations. The parameters are tuned using one set of data with genetic algorithm. The tuned parameters are then used to predict the second set of data. In the simulation, the poly-NRTL model is used to describe the vapor-liquid equilibria. The simulated values match well with the experimental values. The tuned model gives reasonably good results.