Air represents an inevitable medium for the transmission of various environmental pollutants to humans where the main problem is indoor environment in which people spend most of their time. Each person is a source of specific microbiota that is being released into the surrounding space through the respiratory system, also from skin and trough contact with different objects. Due to the current COVID-19 pandemic caused by the SARS-CoV-2 virus, the World Health Organization (WHO) has published various recommendations to prevent the spread of the virus, including a recommendation to wear protective facial masks. Numerous countries, including the Republic of Croatia, introduced the obligation of wearing protective masks while being indoors. Facial masks, apart from the number of virus particles to which the population is exposed, also reduce the number of bacteria. The main aim of this study was to examine the difference in bacterial filtration efficiency of different types of protective facial masks. Furthermore, along with total aerobic mesophilic bacteria and defined bacterial species, filtration efficiency of yeasts and mould was also examined. Air was sampled in kindergarten (groups Bubamare and Ribice) and in elementary school (classes 4.b and 8.b) using MAS-100 sampling device and Tryptic Soy Agar, chromogenic, Sabouraud and blood agar (for each plate it was taken 250 L of air) in February 2021. The first step in each group was to take a sample of air without any facial mask, which represents a control. Next, air samples filtered with a single-layer canvas, surgical, and FFP2 mask settled on sampler head were taken The total number of bacteria, yeasts and mould was determined. In order to determine exactly which bacterial species are present in these groups, the following classical microbiological methods were performed: Gram staining, catalase, oxidase and coagulase test and biochemical test - API Staph. Identification established that bacteria of the genera Staphylococcus and Micrococcus dominate in all groups, while bacteria of the genera Bacillus, Acinetobacter and Corynebacterium were found in significantly smaller number. Also, the results have shown that FFP2 masks are the most effective in filtering bacteria and that a very low number of microorganisms pass through them. Next up, results have shown that surgical facial masks are less effective, while single-layer canvas masks have proven to be the least effective. The same results were achieved with filtration of yeasts and mould, therefore FFP2 mask proved to be the most effective for yeasts and mould filtration too, while the single-layer canvas mask had the lowest efficiency.