To eliminate crosstalk problem among multiple ultrasonic range sensors used in mobile robots, a novel pseudo random frequency-modulated (PRFM) sequence is put forward and used to drive ultrasonic transducers. A PRFM sequence is composed by multiple fixed-width and fixed-amplitude short pulses, but the duration between two neighboring pulses is random. To ensure that the sequence could be applied to fire ultrasonic sensors, its frequency range is designed to meet the bandwidth of ultrasonic transducer. Each ultrasonic transducer is assigned such a unique sequence, so by using correlation technique the transducer can identify if the echoed sequence is emitted by itself, thus the crosstalk problem can be eliminated thoroughly. Real experiments using two Polaroid 600 series instrument grade electrostatic transducers validate the feasibility of the PRFM sequence.