Cellulose based carriers have the potential for sustained release of drugs, which can protect drugs and deliver them to the target site. Herein, BA-loaded cellulose-graft-poly(L-lactic acid) nanoparticles (CE-g-PLLA/BA NPs) were fabricated by employing cellulose (CE) and poly(L-lactic acid) (PLLA) as materials and betulinic acid (BA) as a model drug. Both drug-free and BA-loaded nanoparticles were spherical in shape with a uniform size of 100–170 nm. The release of BA from CE-g-PLLA/BA NPs was relatively slow. In vitro cytotoxicity studies with A549 and LLC cell lines suggested that CE-g-PLLA/BA NPs were slightly superior to BA in antitumor activity and CE-g-PLLA NPs were non-toxic. The antitumor effect of the CE-g-PLLA/BA NPs in a mouse tumor xenograft model exhibited much better tumor inhibition efficacy and fewer side effects than that of BA, strongly supporting their use as efficient carriers for anti-cancer therapy.