In this study, the setting of calcium-sulphate (CS) and -phosphate (CP) based bone cements (BCs) was monitored by ultrasound. The objective was to link acoustic and material properties of ceramic-based BCs from the early stages of the cement curing process. The powder phase of the CS-cement consisted of CS hemihydrate; the CP-cement was a mixture of alpha-tricalcium phosphate, CS dihydrate and hydroxyapatite. For the CS-cement, the acoustic impedance z c(t), the speed of sound c c(t) and the density ρc(t) were measured at the interval of liquid-to-powder ratios LPRs from 0.20 to 3.00 ml/g. For the CP-cement, the acoustic characteristics obtained were the z c(t) and the reflection coefficient R p,c(t), and the LPRs ranged from 0.30 to 0.40 ml/g. The resulting acoustic properties indicated that CP- and CS-cements exhibited distinctly different curing behaviour; while CS-cement expanded, CP-cement shrank with time.