Several brain regions are involved in the learning process that is integrated from sensorial inputs. It is thereafter consolidated in short- (STM) or long-term memory. Serotonin is strongly related to both types of memory, and particularly, to STM, however, its regulatory role is still unclear. In this study, the effects of tryptophan (TRY) restriction on learning and STM were evaluated. Ten Sprague-Dawley female rats were fed with a TRY-restricted diet (0.15g/100g) starting from postnatal Day 21. At 21, 40, and 60 days of age, 5 trials per animal were carried out in a "hard-floor"-Biel maze, after 24 h of water abstinence. The number of errors per trial were registered before reaching the goal. At both 40 and 60 days, experimental rats committed less errors than controls. Likewise, the TRY-restricted group learned the task from the second trial on, whereas controls did not solve it until the third trial. TRY restriction, and therefore brain serotonin reduction, could impair normal cholinergic activity in some areas such as the hippocampus and the cerebral cortex, where involvement in learning and memory is well documented. Morphological and neurochemical plastic events could also be related to the more efficient performance of the task by the TRY-restricted rats.