The speeds of sound of liquid deuterium oxide relative to normal water were measured at 1 atm over the temperature range of 4°–60°C and at pressures up to 1000 bars over the temperature range of 5°–50°C. Three velocimeters were used to measure the sound speeds of deuterium oxide at 1 atm relative to normal water. These three sets of 1‐atm data were fitted to a polynomial equation of temperature with a standard deviation of ±0.09 m/sec. The results of the high‐pressure measurements were fitted to an equation of the form (with a standard deviation of ±0.07 m/sec) (UH2O−UD2O)−(U0H2O−U0D2O) =AP+BP2+CP3+DP4, whereUH2OandUD2Oare, respectively, the speeds of sound in normal water and deuterium oxide (superscript zero denotes 1 atm).A,B,C, andDare temperature‐dependent parameters which were determined by the least‐squares method. Although the values ofU0D2Oobtained in this study are on the average 0.6 m/sec lower than the data of Wilson [J. Acoust. Soc. Am. 33, 314–316 (1961)], the pressure effect on the relative sound speeds from the above equation [(UH2O−UD2O) −(U0H2O−U0D2O)] agree with the work of Wilson to an average of 0.26 m/sec. One atmosphere adiabatic and isothermal compressibilities for deuterium oxide which are reliable to ±0.005×10−6bar−1, were calculated from the sound‐speed data. The results were compared with the data of various workers. The values of isothermal compressibility obtained in this study are systematically higher than the work of Fine and Millero [J. Chem. Phys. 63, 89–95 (1975)] (average 0.05×106bar−1); however, they agree with the data of Millero and Lepple [J. Chem. Phys. 54, 946–949 (1971)] and Emmet and Millero [J. Chem. Eng. Data 20, 351–356 (1975)]to within ±0.02×10−6bar−1.