The mechanism of formation of polyamidoamine(PAMAM)dendrimer-methotrexate(MTX)complex and the release behaviors of MTX from the complex have been investigated．1H-

13C-NMR data confirmed that the formation of PAMAM-MTX complex was due to the interaction between PAMAM external amino groups and the MTX carboxyl groups．The PAMAM-MTX complex was stable in 10 mmol／L

pH 7．4 tris-HCl buffer solution．However．with increasing the ionic strength in the buffer solution

it Was easier for MTX to escape from the complex．which suggested that the interactiOn between PAMAM and MTX was electrostatiC in nature．UV results demonstrated that the hisher the generation of PAMAM

the greater its capacity to carry MTX molecules

e．g．G．5．0 PAMAM and G4．0 PAMAM could load 27 and 14 MTX molecules．respectively.