A series of experiments examined the observing responses as the usage of a cue stiumlus during temporal discrimination learning. The observing response was defined as pressing a lever which presented a cue stimulus but not contingent reinforcers. Five food deprived rats were examined using differential reinforcement of long latencies (DRLL) schedule with a two levers operant chamber. In the first procedure which was presented flicker stimuli automatically, acquired reinforcement effectively. The results showed that flicker stimulus became cue stimulus. The second procedure required a observing response to present a cue stimulus. However, boserving response appeared little numbers. Next, we used more difficult procedures than the secong one. These schedules have long DRLL value. In such schedules, the number of observing responses were more than that in easy schedule.