The　effects　of　La3+　partial　substitution　for　Ba2+　on　crystal　structure　and　dielectric　properties　were　investigated　for　modification　of　Ba5LaTi3Ta7　O30　ceramics.　When　the　substitution　x　＞　0.6,　the　sintering　temperature　obviously　decreased.　Superstructure　peaks　were　observed　for　more　La3+　substitution　(x　≥　2.4).　The　stability　of　the　tetragonal　tungsten　bronze　phase　was　discussed　with　electronegativity　difference　and　tolerance　factor.　Lattice　parameters　decreased　at　first,　and　then　slightly　increased;　while　axial　ratio　decreased　with　increasing　La　content.　Dielectric　constant　slightly　increased　when　x　＜　1.2,　then　gradually　declined　with　the　increase　of　La　substitutions　for　Ba.　Dielectric　loss　was　very　low　except　x　=　2.4.　Temperature　coefficient　of　dielectric　constant　(at　1　MHz)　was　remarkably　improved.　The　variation　of　dielectric　properties　was　discussed　from　the　change　of　crystal　structure　as　well　as　the　effects　of　vacancies　at　A-sites　and　superstructure.　©　Springer　Science+Business　Media,　LLC　2006.