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In this work, the (1-x)CaWO4-xNa2WO4 (x = 0.1, 0.2, denoted as 0.9CW-0.1NW and 0.8CW-0.2NW, respectively) ultralow-loss microwave dielectric ceramics were prepared via solid-state reaction method. Using low melting-point Na2WO4 as sintering aid to prepare CaWO4Na2WO4 composite ceramics, the sintering temperature of CaWO4 was successfully reduced while maintaining excellent microwave performance. The optimal microwave dielectric properties have been achieved at 900 °C for 0.9CW-0.1NW ceramic: εr = 9.0, Q × f = 105660 GHz, tanδ = 1.1 × 10−4 and τf = −35.4 ppm/°C at a frequency of 12.0 GHz. For the 0.8CW-0.2NW ceramic, the optimal microwave dielectric properties have been obtained at 740 °C, with εr = 8.5, Q × f = 97014 GHz, tanδ = 1.2 × 10−4 and τf = −37.4 ppm/°C at a frequency of 11.8 GHz. In summary, both composite ceramics exhibit low sintering temperatures, excellent dielectric properties and chemical compatibility with the Ag electrode. The findings of this study provide an effective approach to prepare novel composite ceramics as promising candidates for LTCC applications.