Two carboxylation processes were carried out to modify multi-walled carbon nanot ube bundles (m-MWNTs). The results showed that both of the m-MWNTs could be high ly dispersed in water with the concentration up to 25 and 15mg/mL in ethanol wit hout obvious deposition or conglomeration over 6 months. FTIR, Raman, TGA and TE M characterizations of the m- MWNTs showed that hydroxyl and carboxyl groups hav e been attached with MWNTs, and that the nanotube structure was only damaged a l ittle after modification treatments in mixed acids over 24h. Above prepared nano tube suspensions in water were successfully used as a filler of thermoplastic PV A composite to enhance its electrical conductivity. The results showed that the addition of m-MWNTs greatly improved the conductivity and the threshold of mass fraction was about 5wt%. The results also proved that purification process was n ot needed because of high purity of the raw MWNTs prepared in our group. Two carboxylation processes were carried out to modify multi-walled carbon nanotube bundles (m-MWNTs). The results showed both both of the m-MWNTs could be high ly dispersed in water with the concentration up to 25 and 15 mg / mL in ethanol wit hout obvious deposition or conglomeration over 6 months. FTIR, Raman, TGA and TE M characterizations of the m- MWNTs showed that hydroxyl and carboxyl groups hav e been attached with MWNTs, and that the nanotube structure was only damaged al ittle after modification treatments in mixed acids over 24h. Above prepared nano tube suspensions in water were successfully used as a filler of thermoplastic PV A composite to enhance its electrical conductivity. The results showed that the addition of m-MWNTs greatly improved the conductivity and the threshold of mass fraction was about 5wt%. The results also proved that purification process was n ot needed because of high purity of the raw MWNTs prepared in our group.