The synthesis and structure of the title complex K2［YⅢ(dtpa)(H2O)］*7H2O (dtpa=diethylenetriaminepentaacetate) were studied. The crystal and molecular structures of the complex were determined by single-crystal X-ray structure analysis. The crystal of the complex K2［YⅢ(dtpa)(H2O)］*7H2O belongs to triclinic crystal system and P(-1) space group.The crystal data are as follows:a=0.9671(2)nm,b=1.1327(2)nm,c=1.3389(3)nm，β=86.76(3)°，γ=68.72(3)°,V=1.3324(5)nm3,Z=2,M=699.53,DC=1.744 g*cm-3,μ=2.586 mm-1 and F(000)=720. The final R and RW are 0.0467 and 0.1195 for 4524(I＞2σ(I)) unique reflections, respectively. The complex anion　［YⅢ(dtpa)(H2O)］2- has a pseudo-monocapped square antiprismatic nine-coordinate structure in which eight coordinate atoms, three N and five O are from a dtpa ligand and one water molecule coordinates to YⅢ ion directly as the ninth ligand.