A supramolecular injectable hydrogel was fabricated. The hydrogel was in situ gelated by the host-guest interaction between alpha-cyclodextrins (alpha-CDs) and methylated poly(ethylene glycol) grafted poly(alpha,beta-malic acid) (mPEG-g-PMA). The hydrogel was characterized by (1)NMR, XRD, DSC, TGA and SEM. The results showed that the polyrotaxanes of alpha-CDs/mPEG-g-PMA acted as physical crosslink sites in the hydrogel. Anti-tumor drug doxorubicin hydrochloride (DOX) was loaded in the hydrogel. The release and anti-tumor effect were studied in vitro. The burst release of DOX was restrained obviously. The sustaining release time lasted more than 3 d and the cell viability decreased greatly. This hydrogel is a promising injectable hydrogel for minimally invasive therapeutic drug delivery.