The aim of the study was evaluation of growth and metabolic activity of Lactobacillus rhamnosus GG during fermentation of leguminous porridges (soybean flour, soybean, chickpea flour, chickpea, white bean, red bean, speckled bean, green lentil, husked lentil, yellow pea), and the evaluation of their stability during storage. A mixture of leguminous sample with water was inoculated after sterilization with equal number of L. rhamnosus GG, to obtain 5 log cfu/g in the porridge. Fermentation was led at 37 °C during 10 hours and storage at 5 °C for 21 days. Monitoring of the lactobacilli counts, pH value, and concentration of organic acids during fermentation and storage was done. Calculation of growth and metabolic parameters during fermentation and storage period was performed by the mechanistic model of Baranyi and Roberts. L. rhamnosus GG was able to grow up to 6.8–7.9 log cfu/g during fermentation, cell density during storage period was stable, except whole soybean, yellow pea and red bean. Metabolic activity of L. rhamnosus GG during fermentation caused decrease of pH value to the final 5.6–6.0, increase of lactic and acetic acid concentration to 89.3–341.7 mg/kg and 129.2–525.2 mg/kg, respectively. During storage period, metabolic activity of L. rhamnosus GG continued.