Polyurethane(PU)-crosslinked multi-walled carbon nanotubes(MWNTs) with different MWNTs content were synthesized, and their morphology and crystallization were investigated. The crosslinking of MWNTs with PU was achieved by reacting MWNTs treated chemically in the mixed acids with prepolymer obtained from a reaction of diisocyanate and polyol. The functioanlization of MWNTs with PU was confirmed by FT-IR, Raman, and XPS measurements, and their morphology was observed by SEM and TEM measurements. Optimum content of MWNTs for PU-crosslinked MWNTs was dependent on an amount of prepolymer and concentration of -OH group in MWNTs. The crystallinity of poly($varepsilon$-caprolactone)-based PU decreased with an increase of MWNTs content, and it was ascribed to the confinement of crystallization of PCL molecules due to the crosslinking of PU with MWNTs.