Flexibility to changing environments is vital for survival and daily functioning. Impaired flexibility is a feature of many pathological conditions, including obsessive-compulsive disorder and schizophrenia, which result in a dissociation between actions and goals. The prevailing theory is that goal-directed actions support flexible behaviour, and impaired flexibility results from habit formation due to extended training, also called overtraining, whereby responding becomes less dependent on outcome value (e.g., compulsive responding).This dual-system theory suggests that overtraining results in subjects adapting less quickly to task changes. Contrasting with this suggestion, previous studies showed that overtraining on an initial two-choice discrimination task produced a faster reversal of responses when the reward contingencies of the choices were reversed.Here, we investigated the impact of overtraining on serial spatial reversal learning in male Lister hooded rats performing a food-reinforced lever-press task. Before each reversal, a control group was trained to a criterion (i.e. ten consecutive correct lever presses), whereas an overtrained group was trained for an additional 100 trials after reaching the same criterion.Overtrained rats learnt to reverse faster than the control group, although both groups had similar error rates. Notably, overtrained rats committed proportionally more perseverative errors but fewer regressive errors. Our findings show that overtraining increases perseveration and behavioural flexibility, as reflected by faster serial spatial reversal learning. We are currently developing a new theoretical account to elucidate why overtraining improves reversal learning and increases perseveration, potentially reshaping our understanding of behavioural flexibility.