Introduction. The characteristics of sponge cakes with partially replaced of wheat flour with milk thistle seed powder are presented in this study. Materials and methods. Milk thistle (Silybum marianum L.) seed powder was used to partially replace wheat flour in sponge cake preparation. Baking loss, moisture content, water activity, volume, porosity, texture, crust and crumb colour, sensory analysis, antioxidant activity, and total phenol content were determined in sponge cake with milk thistle seed powder. Results and discussion. Increasing the level of wheat flour substitution with milk thistle powder from 0 to 20% decreases the volume and porosity of cakes. The addition of milk thistle powder influenced the texture and crumb color of the baked sponge cakes. The hardness and chewiness of baked sponge cakes had an upward trend with increasing milk thistle powder amounts, whereas the cohesiveness, resilience and springiness showed a reverse trend. For the crust and crumb colour the L* and b* values decreased, while the a* value increased, showing that darker, redder and less yellow samples were obtained. The milk thistle addition had a positive effect on the total phenols content by increasing it from 63.93 (control sample) to 121.94 mg gallic acid equivalents, (GAE)/100 g (sample with 20% replacement of wheat flour with milk thistle powder). Simultaneously, the highest antioxidant activity (44.70%) was recorded for the sample with 20% milk thistle seed powder. The sensory analysis pointed out that the sponge cake with the replacement of 5 and 10% wheat flour with milk thistle seed powder was the most acceptable. Conclusions. The incorporation of milk thistle seed powder in sponge cake formulations enriched its biological value in terms of total phenol content and antioxidant activity. However, some technological quality parameters decreased. The sensorial evaluation showed that to produce sponge cakes with high quality, replacement of wheat flour with milk thistle seed powder should not exceed 10%.