In the process of high-level nuclear waste (HLW) disposal, monazite, LaPO₄ is considered as one of the potential phosphate ceramics to immobilize lanthanides and actinides. HLW along with hazardous long-lived nuclides contains elements such as Zr, Mo, etc. in higher wt%. In the current investigation, an attempt was made to introduce “Mo” into the monazite lattice. The phosphomolybdates of the formula La_1−xCa_xP_1−yMo_yO₄, x, y=0.1–0.9 were synthesized by a solution route and characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopic techniques. The phases with compositions La_0.9Ca_0.1P_0.9Mo_0.1O₄, La_0.8Ca_0.2P_0.8Mo_0.2O₄, and La_0.7Ca_0.3P_0.7Mo_0.3O₄ were found to be crystallized in monazite structure. The composition La_0.1Ca_0.9P_0.1Mo_0.9O₄ with X=Y=0.9 crystallized in the scheelite structure. The compositions indicate the immobilization of ∼4.1, 8.5, 12.9, and 42.5 at. wt% of “Mo.” With x, y=0.6, 0.5, 0.4, 0.3, and 0.2, along with the monazite phase, formation of a secondary phase LaP₃O₉ was observed.