The phase compositions and microwave dielectric properties of Ca2(Hf1-xSnx)Si4O12 (0 ≤ x ≤ 0.5) were investigated by the solid-state reaction method. A single-phase ceramic with monoclinic structure was formed in the Ca2(Hf1-xSnx)Si4O12 (0 ≤ x ≤ 0.2) ceramic. At 0.25 ≤ x ≤ 0.5, CaSiO3 and CaSnSiO5 second phases appeared. The microwave dielectric properties of a novel Ca2HfSi4O12 ceramic (εr = 8.1, Q×f = 39,700 GHz and τf = ‒12.7 ppm/°C) were obtained. Partial substitution of Sn4+ for Hf4+ could reduce its relative permittivity and improve quality factor, and the highest quality factor of 49,500 GHz was obtained at x = 0.2. The τf value of Ca2(Hf1-xSnx)Si4O12 ceramics could be controlled to a near-zero value by the CaSnSiO5 second phase when x > 0.3. The optimum microwave dielectric properties (εr = 8.0, Q×f = 37,100 GHz and τf = ‒7.2 ppm/°C) were achieved in the Ca2(Hf1-xSnx)Si4O12 (x = 0.4) ceramic.