A pet safety warning ring comprises a collar body, a vibration frequency sensor, an information transmission module, a warning flash device, a microcontroller chip, a sensing adjustment means and an ultrasonic transmitter. When a pet is moving, the vibration frequency sensor receives a vibration and transmits a message to the warning flash device to achieve the effect of warning a driving car about the existence of the pet. If the vibration frequency sensed by the warning ring reaches a specific value, the microcontroller chip will turn on the ultrasonic transmitter to emit a high-decibel ultrasonic wave, such that the pet will feel uncomfortable. When the pet slows down its movement, the ultrasonic transmitter will stop operating, so that the moving speed of the pet can be controlled to prevent an accident if the pet runs onto a road.