Background: Muffins are sweet, high-calorie baked products whit a typical porous structure and high volume which confer a spongy texture. Because of this texture and good taste, these products are highly valued by consumers. But muffins have low nutritional value. Objective: The aim of this study was to develop the technology of muffins as a functional product with hepatoprotective activity using defatted milk thistle powder (DMTP). The addition of this dietary supplement was carried out by partial replacement of flour in the classic baking formulation. Methods: Physical-chemical and sensory analyses were performed to evaluate muffins either with or without defatted milk thistle powder. The moisture sorption isotherms of porous structure were determined by the gravimetric method on vacuum equipment with McBen quartz spring balances over 0.05-1.0 water activity range, and the data fitted to models to Guggenheim-Anderson-de Boer (GAB), Brunauer-Emmet-Teller (BET). Results: It has been established that the addition of milk thistle powder reduces baking, increases the drying out of products and increases the water-holding capacity, as well as increasing the volume of muffins and crumbs density. The microstructure of the muffin was examined using a moisture sorption isotherm. The moisture sorption isotherms of muffin samples presented a sigmoid shape and belong to type II of BET classification. The hysteresis loops of the samples are almost the same, which indicates similar structural data. The value of the monolayer according to BET models varied in the range 2.38–4.59 g H₂O/100 g^-1 of dried sample, showing a slight decreasing trend for muffin with DMTP. The GAB model accurately fits the adsorption isotherms in the water activity range from 0.05 to 0.9. The parameter K calculated by this model, which reflects the interaction between water molecules and absorbents in multilayers, turned out to be slightly higher for the sample with DMTP. The sensory results from consumer evaluation indicated that both samples are characterized by the traditional pleasant appearance of the muffin, without visible flaws, pleasant taste, and a good flour aroma. Conclusion: The result was a muffin with the same texture and sensory characteristics, but with a potential functional food.