The linear thermal expansion coefficients of theaandcaxes of bismuth have been measured from 80°K to 540°K by mechanical means. These same coefficients were determined over a more limited range of temperatures by single crystal and powder x‐ray methods. The mechanical and x‐ray values did not differ significantly. The expansion coefficient for thecaxis was found to be 16.6±0.4×10−6(C°)−1at 100°K, 17.3±0.2×10−6(C°)−1at 150°K, and 17.6±0.2×10−6(C°)−1at 540°K. For theaaxis the expansion coefficient was 10.8±0.3×10−6(C°)−1at 100°K, 11.6±0.2×10−6(C°)−1at 150°K, and 11.8±0.2×10−6(C°)−1at 540°K.