The aim of this work was to determine the inﬂuence of various variants of bioleaching on effectivity of releasing chosen critical metals: rhodium, cadmium, indium, niobium and chromium from ashes which are a byproduct of municipal waste and sewage sludge thermal processing. The research was conducted in 3 variants that considered different process factors such as temperature (24ºC and 37ºC), mixing intensity and aeration. After 5 days of the process the analyses were made of metals content, sulfate concentration, pH, general number of bacteria number, index of sulfur oxidizing bacteria. The best results of bioleaching were achieved by running the process at the temperature of 24ºC with aeration. The efﬁciency of rhodium and cadmium release from the byproduct of municipal waste thermal processing was above 90%. The efﬁciency of indium and chromium release reached 50–60%. Only niobium leached better in mixing conditions. The byproduct of sewage sludge thermal processing was far less susceptible to bioleaching. The highest effectivity (on a level of 50%) was reached for indium in temperature of 24°C with aeration. The efﬁciency of bioleaching depended on waste’s physiochemical properties and type of metal which will be released. Aeration with compressed air had a positive inﬂuence on the increase of sulfur oxidizing bacteria what corresponded with almost double increase of sulfate concentration in leaching culture. Such conditions had a positive inﬂuence on the increase of the efﬁciency of bioleaching process. Heightening the temperature to 37°C and slowly mixing did not impact bioleaching in a positive way.