Ultrasonically induced birefringence of two rodlike particles of the hematite sols and the poly(tetrafluoroethylene) latex was investigated as a function of volume fraction, ultrasonic intensity, and frequency. The negative birefringence was observed for both samples, and the birefringence was proportional to the volume fraction and the ultrasonic intensity. The frequency dependence of the birefringence was observed in the wide ultrasonic frequency range from 5 to 225 MHz and did not agree with the Oka theory. The modified Oka theory for disclike particles was extended in view of application for rodlike particles. The birefringence measured was several tens of times larger than that calculated from the modified Oka theory for rodlike particles. The orientational relaxation time of the two particles estimated from the trace of the transient birefringence can be expressed in the form of the Debye-Einstein equation.