Tactile dots located on operation keys of consumer products such as cellular phones contribute to improving accessibility for older people and people with visual impairment. The Japanese Standards Association (2000) and the International Organization for Standardization (2011) standardized tactile dots. However, reliable data on the appropriate sizes and the shapes was not necessarily available. The purpose of this study is to evaluate influences of the height (0.1, 0.3, 0.55, and 0.75 mm) and the tip radius of curvature (0.1, 0.3, 0.5, 0.7, and 0.9 mm) of tactile dots on the operational performance of cellular phones in younger and older people. Sighted younger and older participants, whose hand was covered by a curtain, operated cellular phones with a tactile dot on its key 5 and without a tactile dot. As the result, both participants performed better at a particular height with larger tip radius of curvature. Furthermore, older participants operated better at high dots like 0.55-0.75 mm. In contrast, younger participants performed better at 0.3 mm and relatively poorly at 0.1 mm and 0.75 mm. Thus, comparatively high tactile dots are useful for improving the accessibility of products for the older and there is an appropriate height range for the younger.