These days, according to surprising development of communication enterprises, every soft of devices is getting smaller and cheaper. Among these Devices, microwave dielectric ceramics are studied and progressed briskly as the materials of dielectric resonator. Dielectric properties of BaO-S $M_{2}$ $O_{3}$-Ti $O_{2}$, one of the BaO Lnsub 2/ $O_{3}$-Ti $O_{2}$ (Ln=La, Sm, Nd, Pr…) system, synthesized by solid-reaction and coprecipitation method were investigated. Disk-type samples were sintered at 1250-1400.deg. C for 2hrs. As a result, single phase was not synthesized in both method. First created the second phase of S $M_{2}$ $Ti_{2}$ $O_{7}$, and then the last phase of $Ba_{3.75}$S $m_{9.5}$ $Ti_{18}$ $O_{54}$, Ti $O_{2}$, and $Ba_{2}$ $Ti_{9}$ $O_{20}$. When the sample was sintered at 1280.deg. C (in solid reaction method) and at 1310.deg. C (in coprecipitation method), it obtained highest dielectric constant (72.96 and 71.70, respectively) and high Q value. Above that temperature, dielectric constant and Q value decreased because of lattice defect according to oxygen vacancies........