Objective      To establish a model of classical conditioned pupillary dilation in conscious and fixed cats and to analyze the related acquisition rule.        Methods      With sound as the conditioned stimulus (CS) and tail shock as the unconditioned stimulus (US)

3 health adult cats were trained with CS-US intervals 0 ms and 900 ms separately. With an infrared pupil measurement device

the pupil area changes were recorded in a real-time manner and then to judge whether a cat acquired classical conditioned pupillary dilation.       Results      The cats acquired classical conditioned pupillary dilations in the 900 ms CS-US interval model. After 10 times and 30 times pairing training

the acquisition rate was 26.67% and 53.33%

respectively. After 50 times pairing training

the acquisition rate was 76.67%. In the following 30 times fading training

the acquisition rate showed a decrease trend.       Conclusion      The acquisition of classical conditioned pupillary dilation in cats is related to CS-US interval and CS stimulus amount. This kind of reflex can be acquired in a small amount of pairing training

but fades quickly.