For low-vision people and elderly people with decreased vision and cognitive function, the legibility of signs (character size, position, etc.) is an important issue. Graphic floor signs are considered more effective for low-vision people and elderly people than typical hanging signs because they are closer to pedestrians and can be larger in size. There is a growing number of improved graphic floor signs, but there are no guidelines for character sizes, colour scheme, and layout. Therefore, this study considers the character size ofgraphic floor signs that are legible for elderly people. In this study, we aimed to verify the legibility of characters installed on the floor. The test was conducted on 30 non-elderly and 30 elderly people, about Japanese Industrial Standards (JIS) S 0032 “Guidelines for the elderly and people with disabilities - Visual signs and displays -Estimation of minimum legible size for a Japanese single character”. Experiments on minimum legible sizes of characters and experiments on readability were conducted in that order. In the experiment on the minimum legible sizes of characters, we found that the minimum legible sizes of characters written on the vertical surface can be converted to the minimum size of legible characters written on the floor surface by multiplying with the coefficient of minimum legible characters on the floor surface by 2 to 3 times. In the experiment on readability, we found that the optimum character sizes are about 90 mm and 80 mm in height at a minimum for vertical and horizontal characters, respectively. These results showed that the optimum size of characters on graphic floor signs is about 90 mm.