Dielectric characteristics of composite ceramics in the system Ba(Mg1/3Ta2/3)O-3-BaO . Nd2O3 . 5TiO(2) were investigated to search for a new candidate system for microwave dielectric ceramics with modifiable dielectric constant, low dielectric loss and small temperature dependence. The dielectric constant could be adjusted in the range 25-81 by controlling the concentration of BaO . Nd2O3 . 5TiO(2), while the dielectric loss remained of the order of 10(-4) for some compositions. Moreover, the dielectric properties in the present system could be significantly improved by post-densification thermal treatment.