The purpose of this research is to develop a protocol which can quantitatively evaluate cognitive ability that is needed when elderly people use mobile phone. Since previous methods for measuring the cognitive ability of elderly people was mainly for clinical evaluation, they would not be adequate to measure cognitive ability for mobile phone development. Therefore, this study suggests cognitive areas which are necessary to use the mobile phone based on the existing evaluation tools. The cognitive areas consist of language, visuospatial ability, memory, executive function and perception. New questionnaire was developed to evaluate the individual cognitive ability for the elderly. They include 9 questions for button comprehension test, 8 for icon button comprehension test, 10 for vocabulary comprehension test, 8 for menu comprehension test, 3 for icon size test, and 2 for font size test. The protocol can be used in the field although further modification may be necessary for betterment.