Nanofiltration (NF) is considered to be an intermediate process between reverse osmosis (RO) and ultrafiltration (UF). In the present work, separation data obtained for nickel sulfate-water and nickel chloride-water systems, using an N, O-carboxymethyl chitosan (NOCC)-polyether sulfone (PES) composite NF membrane, are analyzed with the help of two nonlinear membrane transport models, viz., combined film theory-solution-diffusion (CFSD) model and combined film theory-Spiegler-Kedem (CFSK) model. The membrane transport parameters and mass transfer coefficient (k) are estimated, simultaneously, from both the models using the Levenberg-Marquardt method. The k values estimated from two models show a variation that may be attributed to the presence of reflection coefficient in the Spiegler-Kedem model. Though both the models predict the membrane performance reasonably, the values of CFSK model are more accurate in the present case. Hence, it can be suggested that CFSK model may be the better method for estimating the membrane transport parameters and k. Various parameters estimated from the above models are used to find the enrichment factors, concentration polarization modulus and Peclet numbers for both the systems.