The crystal of potassium lanthanum metaphosphate with composition KLaPO34 belongs to monoclinic system. The space gr oup is P21 with lattice parameters α= 8.106(3)?, b= 8.551 (2)?, c = 7.326(3)?, β = 92.18(6)°. Two molecules are contained in the unit cell. A fullmatrix, least square refinement gave R=0.061, Rw = 0.062 for 1026 independent reflections. The basic structural units are helical ribbons, (PO3)n, formed by cornersharing tetrahedra of PO4. The LaO8 dodecahedra are isolated without sharing any O atom with each other, and K atom locate on the center of irregular interstitial polyhedra. The shorhest La-La distance is 7.063?.