OBJECTIVES: Bituminous materials, such as tack coat, are utilized between pavement layers for improving the bond strength in pavement construction sites. The standards regarding the application of bituminous material are not clearly presented in the Korean construction guideline without RS(C)-4. Hence, the objective of this study is to determine the optimum content of bituminous materials by analyzing interlayer shear strength (ISS) from the direct shear tester, which was developed in this research. The shear strength of tack coat was defined with the sort of bituminous materials. METHODS : The mixtures for the shear test were made using marshall mix design. The specimens were vertically and horizontally separated for the direct shear test. The separated specimens were bonded using bituminous material. The objectives of the experiment are to determine the performance of bond and shear properties resulting from slippage, rutting, shovel, and corrugation of asphalt pavements. A machine based on the Louisiana interlayer shear strength tester (LISST) of NCHRP Report-712 was developed to determine the ISS. The applied types of tack coat were RS(C)-4, AP-3, QRS-4, and BD-coat with contents of 0.3ℓ/m2, 0.45ℓ/m2, 0.6ℓ/m2, and 0.8ℓ/m2, respectively. RESULTS: Table 2 gives the results of the direct shear test using the developed shear machine. The BD-coat type indicated the highest average ISS value compared to the others. Between the surface and binder course, optimum tack coat application rates for AP-3, RS(C)-4, QRS-4, and BD-Coat were 0.6ℓ/m2, 0.3ℓ/m2, 0.6ℓ/m2, and 0.45ℓ/m2, respectively. These optimum contents were determined using the ISS value. CONCLUSIONS: The ISS values of AP-3, RS(C)-4, and QRS-4 showed similar tendencies when ISS increased in the range 0.3~0.6ℓ/m2, while ISS decreased when the applied rate exceeded 0.6ℓ/m2. Similarly, the highest ISS value of the BD-coat was observed when the applied rate was 0.45 ℓ/m2. However, shear strength was similar to the maximum value of ISS when the tack-coat application rate of BD-Coat exceeded 0.45ℓ/m2.