A precipitation reaction between a lead-nitrate solution and oxalic acid was carried out with and without ultrasound, and the Effect of ultrasonic irradiation in solution was investigated. The oxalate precipitates were a mixture of Pb oxalate and an X-phase, which seems to be a lead salt containing C2O42-, NO3-, and OH-. It was found that irradiation with ultrasound during the precipitation reaction accelerated the formation of the X-phase.