The neuronal activity in SI cortex was collected when monkeys performed a haptic-haptic (HH) delayed matching-to-sample task.We found that in trials with correct task performance a substantial number of cells showed significant differential neural activity only when the monkeys had to make a choice between two different haptic objects.Analysis of incorrect trials showed that such a difference in neural activity was significantly reduced.However, the choice differential neural activity was barely observed in monkeys who performed a control task that was identical to the HH task but did not require the animal to either actively memorize the sample, or make a choice between the two objects at the end of the trial.Combining all the above results together, we believe that the differential activity may be a neural correlate of decision making, and thus conclude that some SI cells function particularly in the process of decision making when the animal has to make a haptic choice.Our findings indicate for the first time that primary sensory cortex may play an important role in decision making.