Diagnosis and treatment planning is initial step to fabricate removable partial denture, and one of most important factor influencing the prognosis. Partial edentulous patients have various condition of remaining teeth and oral mucosa. Therefore, for the proper diagnosis and treatment planning for each patient, getting many informations from patients during initial examination and fabricating accurate diagnostic cast are required. Especially, because the use of various diagnostic tools and surveying of diagnostic cast will be a guide for the abutment teeth selection, oral preparation and design of partial denture, dentist should understand and be able to apply this procedure during diagnosis.