The effect of BaCu(B 2O 5) (BCB) on the sinterability, microstructure and microwave dielectric properties of Ba 4Sm 9.33Ti 18O 54 (BST) has been investigated. Dilatometric measurements reveal that the sintering temperature of BST can be reduced by the addition of BCB. Microstructural analysis shows abnormal grain growth with large amount of BCB. A ceramic composite with Q × f = 4000 GHz, ɛ r = 52 and τ f = −29 ppm/°C which can be sintered at 950 °C is obtained when 10 wt% BCB is added to BST. EDS analysis shows that the composite is chemically compatible with silver.