N-triethyl chitosan (TEC) has recently been proven to be an efficient polymer for improving transport of hydrophilic drugs. Thus, in order to evaluate its gene delivery efficiency, TEC is assembled with Enhanced Green fluorescence protein plasmid DNA (pEGFP) at different polymer to plasmid (N/P) ratios to form TEC/pEGFP nanoparticles. Photon correlation spectroscopy is used to evaluate nanoparticles size and zeta potential. The transfection efficiency and cytotoxicity in gene delivery to AsPC-1 cells (human pancreatic cancer cells) are evaluated via fluorescence microscopy, flow cytometry and MTT assay. Also parameters such as cancer cells’ mean fluorescence intensity (MFI) and cell size changes after transfection are assayed. The results indicate that the incorporation of pEGFP in TEC can form charged nanoparticles at N/P ratios from 10 to 40. Increasing the N/P ratio increases transfection efficiency, MFI, cell size and cytotoxicity. At N/P ratio of 10, transfection increased up to 11.12 fold with the least cytotoxicity. Considering that mathematical models can be used to understand and predict consequences associated with nanomedicine, the relation between TEC /pDNA nanoparticles charge ratio, cell transfection and toxicity was evaluated for the first time with interpolation polynomial method.