In this study, a natural polymer, chitosan (CS) has been converted through modified procedures into a water soluble carboxymethyl chitosan (CMCS). This was fully characterized by numerous techniques, including Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and two dimensional wide-angle X-ray scattering (2D-WAXS). The anticancer activity of the obtained CMCS was investigated in comparison with its parent compound, CS using mice bearing Ehrlich ascites tumour cells (EAC). It has been found that treatment with CMCS and CS has significantly inhibited tumour growth in a dose-dependent manner, which indicates their significant antitumor activity. However, CS showed to be more superior, as an anticancer agent, over CMCS under the same experimental conditions. Biochemical assays also revealed that treatment with CMCS and its parent polymer (CS) has led to an augmentation of the antioxidant defense system without affecting lipid peroxidation in EAC-bearing mice.