Poly(ethylene succinate-co-decamethylene succinate) (PEDS) is a novel biodegradable copolyester with a relatively slow crystallization rate. PEDS/carboxyl-functionalized multiwalled carbon nanotube (f-MWCNT) nanocomposites were prepared to enhance the crystallization rate and improve the mechanical properties of PEDS from a practical application viewpoint. The effects of f-MWCNTs on the crystallization behavior, morphology, and mechanical properties of PEDS were investigated with various techniques. The f-MWCNTs distributed homogeneously through the PEDS matrix at the f-MWCNTs content of 0.2 wt %, while at the f-MWCNTs content of 0.5 wt % some aggregations developed. The thermal stability of the nanocomposites did not obviously change by f-MWCNTs. The nonisothermal and isothermal crystallization behaviors of PEDS were accelerated by f-MWCNTs, while the crystallization mechanism of the PEDS matrix remained unchanged. The crystal structure and crystallinity of the PEDS/f-MWCNT nanocomposites were similar to those of PEDS. Moreover, the storage modulus of the nanocomposites was significantly increased compared with that of PEDS, whereas the glass transition temperatures were slightly higher than that of PEDS.