A laboratory study was carried out to investigate the change of ultrasonic velocity as a function of temperature for fluid mud (i.e., suspension). Pulse transmission technique with ultrasonic wave was used for ultrasonic velocity measurement. The five samples for fluid mud were prepared for concentration range of $30.6{\%};(1.24;g/cm^{3};in;density),;23.3{\%};(1.19;g/cm^{3}),;11.5{\%}(1.10;g/cm^{3}),;7.8{\%};(1.08;g/cm^{3}),;and;3.8{\%};(1.05;g/cm^{3})$ by weight. The ultrasonic velocity in fluid mud was investigated to increase $(approximately;2.83;to;4.95;m/s/^{circ}C)$ with increasing temperature, due to the effect of viscosity and compressibility of water with changing temperature. But the increasing rate tends to decrease at temperature higher than $30^{circ}C,$ caused by the effect of viscosity. The concentration of fluid mud more affect to the ultrasonic velocity at higher temperature range than that at lower temperature. Overall the temperature effect on the ultrasonic velocity in fluid mud was a similar rate as for distilled water and seawater, suggesting fluid mud significantly depends on the behavior of water.