The acquisition and retention of information by the nervous system are major processes of learning. Habituation is a simple learning process that occurs during repeated exposure to harmless stimuli. C. elegans is habituated when repeatedly given mechanical stimuli and recover from the habituation when the stimuli are stopped. A habituation abnormal mutant was isolated and assigned to a new gene hab-1 whose mutation causes slow habituation. The hab-1 mutant phenotype is remarkable at short time interval stimuli. However, hab-1 mutant worms show normal dishabituation. Ablations of neurons constituting the neural circuit for mechanical reflexes did not abolish abnormalities caused by the hab-1 mutation.