Estimation of organ dose from ionizing radiations requires mathematical human phantoms. However, there are some technical difficulties in determining the parameters for mathematical phantom from the actual data on human physique even if we can use the MIRD phantom as a good reference. Difficulties are mostly due to complexity in mathematical expressions of organs. A method proposed here for avoiding this difficulty is to express human body with a system of 3-dimensional picture elements. Each element is assigned to a symbol that corresponds to an organ according to the location of the element in the body. A specific spatial configuration of those symbols composes a “symbol phantom.” The symbol phantom is useful and flexible from the following reasons, 1) its transversed section image can be readily compared with that obtained by medical imaging devices like NMR-CT, 2) modification of the phantom can be done by using usual word-processor techniqe and 3) a more convenient and faster sorting procedure can be achieved in a Monte Carlo calculation.