Mushrooms (Agaricus bisphorus) were osmotically dehydrated in sugar beet molasses solutions at concentrations of 60%, 70% and 80%d.m., at operating temperatures of 25 °C, 35 °C and 45 °C during 0.5h, 1h, 1.5h, 2h, 3h, and 5 hours. Moisture content, water activity (aw), microbiological parameters (total plate counts, Enterobacteriaceae, total yeasts and moulds count) and content of mineral elements (potassium, magnesium, iron and calcium) were determined in the osmodehydrated mushroom samples. Response surface methodology and analysis of variance were selected to estimate the main effects of the process variables (temperature, time, concentration) on process performance and selected mushroom attributes (microbiological counts, chemical composition and mineral content). Increase in the values of applied osmotic process parameters led to the significant increase in the content of minerals (for example, an increase in K and Ca content by 269.42% and 939.03%, respectively) and a decrease in aw values (from 0.941 to 0.811), decrease in microbiological load and relative protein content (decrease by 33.07%), indicating a possibility for prolonged shelf life and suitability for further processing. The osmodehydrated mushrooms could be considered as ingredients for new functional (semi)products due to improved nutritive profile.