K4Fe4P5O20 shows an interesting natrolite-like structure with a spin-tetrahedron lattice built by mixed valence Fe ions. Single crystals of the title compound are successfully grown by the flux method using KF as flux. Magnetic results combined from magnetic, heat capacity, and (57)Fe Mössbauer spectra measurements show that K4Fe4P5O20 possesses a short-range magnetic ordering at ∼13 K and a long-range ordering at ∼7 K. Magnetic anisotropy of K4Fe4P5O20 is observed between H‖c and H⊥c, suggesting that the c-axis is the magnetic easy-axis. The spin arrangements in the system are suggested to be ferrimagnetic along the natrolite chains.