I n the process of drilling, drilling fluid has a very important role, Starting from the initial drilling until the drill reaches the destination. Determination of the composition and selection of the type of a drilling mud that will be used in the drilling operation is one part that determines the success of drilling operations and to avoid the difficulties and potential problems that may arise. One of potential failure is the loss of drilling mud that caused the error of determining the composition of the mud, One of methods to prevent and cope loss of drilling mud is to use LCM. This thesis aims to study about testing Fiber Mat as LCM and its influence on the rheological properties of the Smooth Fluid drilling based mud with two types of concentration, which is 70% -20% and 80% -20%. Media filter for examined the lost Circulation are sand and paper. The results obtained in this study are substantially the Fiber Mat has a role in the changing of rheology drilling mud properties, as the price of density and viscosity increases as theaddition of LCM, The use of Fiber Mat is very effective in tackling Lost Circulation, although the price of mud loss with sand filter is very large compared to the paper, this is already a reasonableness because sand porosity and permeability are better than paper. Changes that occur in general is not significant and damaging the base price of the properties and specifications of mud itself and can still be controlled by adding certain addictive to keep the mud remains ideal.