Water-soluble, partially hydrophobized derivatives of carboxymethylcellulose (CMC) were prepared by the transesterification reaction using the methyl ester of rapeseed oil (MERO). The chemical modification was performed in reaction media H2O/DMF with and without K2CO3 as catalyst, at various reaction conditions and using microwave radiation with controlled power as heating source. The obtained hydrophobically modified carboxymethylcellulose (HM-CMC) derivatives were characterized by FT-IR spectroscopy. The surface-active and viscometric properties of aqueous solutions of unmodified CMC and its HM-CMC derivatives were investigated. The surface-active properties were studied by surface tension, critical micelle concentration and emulsifying efficiency. The complexation of CMC or some HM-CMC derivatives with cationic surfactants - tetraalkylammonium bromides (C(n)TAB) in aqueous medium was studied by measuring the surface tension. The studied derivatives showed, in spite of moderate surface tension-lowering effects, excellent emulsifying activity for 'oil in water' type emulsions comparable to that of the commercial emulsifir Tween 20. The viscometric properties were investigated in the dilute domain. For all HM-CMC solutions the intrinsic viscosities were distinctly lower than for CMC probably due to molecular degradation. The increased Huggins constant of some of the derivatives are indicative of intramolecular hydrophobic interactions. The results suggested that the HM-CMC derivatives and their complexes with C(n)TAB surfactants can be exploited as potential biosurfactants in various industrial applications.