To investigate the hygienic environment in Peru, we visited Cusco sewage treatment plant. The altitude of Cusco sewage treatment plant is 3,193 m being considered that it is one of the treatment plants installed at the highest elevation in the world. It is the newest plant in Peru and the present facility has run since 2014. The treatment type is trickling filter with PVC media. One of the features for being installed at high altitude is installing blowers to supply oxygen despite that trickling filter substantially does not need aeration. It is because of the low oxygen concentration in the air at high altitude. It should be noticed that the plant was entirely controlled by modernized and sophisticated system despite that it was built in developing country.