The linear compressibility of cubic sodium tungsten bronze NaxWO3 (x = 0.72) is (-8.56 ± 0.54) . 1012 Pa-1; the linear compressibility of type I tetragonal bronze (x = 0.46) is (-20.2 ± 1.3) . 1012 Pa-1 parallel to the a axis and (+4.17 ± 1.9) . 1012 Pa-1 parallel to the c axis. The compressibility of cubic bronze decreases somewhat with increasing pressure (in the range 0-250 mPa). The compressibility was directly measured optically.