This study suggests a quantitative evaluation method of joint roughness coefficient (JRC). It was accomplished by using several statistical parameters to the 10 standard profiles. The results show that some of these parameters (Root mean square gradient, Structure function, and Fractal dimension) are suitable to represent the roughness characteristics. With these selected parameters, further studys have succeeded to examine the variance upon scale effect. The result shows that the fractal dimension is the most correlated parameter of all to JRC. The modified empirical equation of shear strength by introducing fractal dimension to determine JRC was suggested. To prove its validity and to examine the applicable limit of the estimated strength by this equation, the values were compared to those obtained in laboratory works. The results show that the quantification procedure for JRC permits more reliable results when the scale effect is considered. The equation which relates normal stress to shear strength of natural joints developed in gneissic rocks is also suggested. This provides inexpensive method to evaluate rock mass porperty and it can be applied to usual engineering practice. (Author).