For medical workers, ultrasonic phantoms are used not only for training on ultrasonic diagnostic equipment, but also to aid ultrasonic-guided needle and blind catheter insertion procedures. The target values of the acoustic characteristics of the phantoms are required to simulate the characteristics of human soft tissue. In this paper, we propose a phantom made of sodium alginate, calcium sulfate dihydrate, trisodium phosphate dodecahydrate, glycerol, and water. The characteristics of the phantoms were evaluated principally by an ultrasonic propagation speed, an attenuation coefficient, and acoustic impedance The optimal preparation conditions of the phantom in this study were to mix sodium alginate, trisodium phosphate dodecahydrate, calcium sulfate dihydrate, glycerol, and water in the ratio of 1 : 2 : 1 : 10 : 50, respectively. The proposed phantom was able to obtain values close to the targets.