The resonance behavior and the electric equivalent circuit of the ringed-electrode piezoelectric sensor (REPS) operating in liquid phase have been studied. The results indicate that the REPS can be used to investigate a solution's properties and mass loading on a quartz surface under different conditions. Using the change in the liquid's conductivity the critical micellar concentration (CMC) of cetyltrimetylammonium bromide (CTMAB) has been measured by the REPS. The result corresponds well with the reference data. Based on the mass effect, the adsorption process of CTMAB onto a quartz surface has been monitored in situ and the adsorption density has been investigated. The rate of CTMAB's being adsorbed onto the quartz surface increases when CTMAB concentration increases. In addition, the adsorption density (adsorbed mass per unit area of CTMAB) is affected by the ion strength of solution. The higher the ion strength in the test solution, the greater is the adsorption density of CTMAB on the quartz surface. It has been shown that the REPS is a useful tool for studying quartz/solution interface interactions in real time.