The objective of the study was to determinate the effect of heat pre-treatment, level of size reduction, and drying method on the content of bioactive substances, i.e. betalain pigments and antioxidants in dried red beets, Bikores v., as well as polyphenolic in dried celeriac, Feniks v.. The dried red beet contained red pigment amounts ranging from 5.25 to 10.64 mg/g d.m., yellow pigment amounts from 2.62 to 6.20 mg/g d.m.; its antioxidant activity was from 58 to 94 μM Trolox/g dm. Those values varied in a wide range depending on the heat pre-treatment, the degree of size reduction, and the drying method. The content of polyphenolic content in dried celeriac varied, with the same variables applied, between 17.5 to 23.5 mg/g d.m, expressed in chlorogenic acid/g d.m.