M ask is one of a Protective Equipment required by workers in the medical field. Forsuch workers, mask serves the function of protecting the lungs from inhalation ofmalicious diseases or bacteria. The following laboratorial and experimental researchis aimed to determine the safety level of mask used in the medical field service. Theresearch will be performed by applying either side with Microorganisms andinspecting the other side after 1 - 3 hours. The first stage of the application shallconsist of 5 types of microorganisms which are Bacillus subtilis, Staphylococcusaureus, Haemophilus influenzae, Streptococcus mutan, and Mycobacteriumtuberculosis which are applied to the outer layer of the mask and is then left for 1hour, followed by rubbing the sterilized cotton bud into the inner side of the mask inwhich it is then stored in a tube filled with Brain Heart Infusion (BHI) liquid. Theresult of the application will be cultivated by rubbing the BHI infused cotton bud intoa solid blood agar medium. This is followed by gram colouring in order to find outthe type of bacteria present. Similar treatment shall be performed following the 2ndhour and the 3rd hour. From the observation of the 1st hour, all eight types of maskwere able to be penetrated by Bacillus subtilis bacteria, and on the 2nd hour - 1 typeof mask was able to be penetrated by both Bacillus subtilis and Haemophilusinfluenzae bacteria, whereas on the 3rd hour - 3 types of mask were able to bepenetrated by Bacillus subtilis, Staphylococcus aureus and Haemophilus influenzaebacteria. As per the data obtained, it can be concluded that not every mask is capableof properly protecting the user from malicious bacteria within certain area, as such,attention regarding the usage of proper and safe mask must be exercised in the fieldof medical service.