Latex-blended nanocomposites of monodisperse polystyrene particle (PS) and multi-walled carbon nanotube (MWCNT) were prepared, and the morphology and rheological properties of the nanocomposites were investigated to elucidate the effect of treatment method on the dispersion of MWCNTs. Several different ways of MWCNT treatment such as acid treatment, ultrasonic treatment and combined treatment of the two were employed to intend to improve the dispersion state of highly entangled MWCNTs. The nanocomposite prepared with either acid treatment or ultrasonic treatment showed substantially increased rheological properties with increasing MWCNT content, indicative of good dispersion of MWCNTs. However, the nanocomposite prepared with combined treatment of the two showed only slightly increased rheological properties with MWCNT content due to the breakage of MWCNTs, although the highly dispersed state of shortened MWCNTs was maintained.