INTRODUCTION: Autophagy is a cellular recycling mechanism essential for maintenance of cell homeostasis and viability, especially during stress conditions; hence, autophagy is involved in a number of physiological and pathological processes. Autophagy is thought to be involved in anti‑aging and neuroprotective effects of caloric restriction, Sirtuin 1 activation, inhibition of insulin/ insulin-like growth factor signaling, and administration of rapamycin, resveratrol, and metformin. The ketogenic diet mimics the biochemical actions of fasting and exerts many physiological and cellular responses similar to those evoked by intermittent energy restriction. Despite this, the relationship between nutritional ketosis and autophagy has been a largely unexplored field. AIM(S): The aim of this study was to verify the hypothesis that ketogenic diets affect the process of autophagosome formation in the hippocampus and/or cerebral cortex. METHOD(S): 9-week-old male mice were fed with one of two differently composed ketogenic chows – based on the fat of either animal or plant origin (KA, KP respectively) or with standard rodent chow (SD) – for 6 subsequent weeks. Western blotting, (LC3, p62), QRT‑PCR (LC3A, LC3B, p62), and confocal microscopy (LC3 puncta) were employed to monitor autophagy in hippocampal and cerebrocortical samples. RESULTS: Western blot results revealed increased levels of LC3 II protein – a marker of autophagosomes – in the hippocampus and frontal cortex of mice treated with the ketogenic diet. This observation was confirmed by the evaluation of a number of LC3 puncta with immunofluorescence microscopy. The size of this effect was dependent on the composition of the diet. CONCLUSIONS: This study reports, for the first time, an upregulation of autophagosome synthesis in the brain of animals fed with the ketogenic diet. Our results make a significant contribution to the understanding of the mechanisms of ketogenic diet action. FINANCIAL SUPPORT: This research is supported by the National Science Center grant no. 2017/01/X/ NZ3/00984.