Tetragonal tungsten bronze (TBB) type niobium compounds Sr6Nb10O30 and a solid solution series Ba6-xLaxNb10O30 (x = 0, 1, 2, 3) were synthesized and their resistivity was measured in the temperature range 10-300 K. The Sr compound is a semiconductor, the high temperature data (100 less than or equal to T less than or equal to 300 K) for which can be fitted to the T-1/4 law. Ba6Nb10O30 also is a semiconductor, but with a different temperature dependency. La-substitution in the Ba compound caused a conduction mechanism to change from semiconducting (x = 0) to metallic (x greater than or equal to 1).