This paper presents the basic knowledges to evaluate the slipperiness of bathroom floors and bathtub bottoms from a viewpoint of safety. First, the measuring method of slip resistance under the condition that the liquid like water, liquid soap, etc were existed among naked foot and bathroom floor or bathtub bottom, was studied. As a result of this study, the appropriate measuring method using O-Y・PSM (O-Y Pull Slip Meter) which was developed by the author, and the appropriate physical value C. S. R・B (Coefficient of Slip Resistance of Bathroom Floor) which indicate the slipperiness of bathroom floors and bathtub bottoms, was obtained. Second, the relation between the easiness to cross the bathtub's edge and its sectional proportion, was studied. And based on the result of this study, 3 proportions which will be used at the sensory test about the evaluation of slipperiness reported at Part 2, was settled.