Abstract: In order to study the effect of ultrasonic vibration assisted casting on the structure of the steel, 43MnS steel specimens for automobile connecting rod were prepared by conventional casting and ultrasonic vibration assisted casting, and the microstructure and sulfide were tested and compared. The results show that the microstructure of the specimen is obviously refined by ultrasonic vibration assisted casting, and the sulfide changes from long strip to fine particle. The sulfide aspect ratio of 43MnS steel by ultrasonic vibration assisted casting is 1.05, which is approximately equiaxed. Compared with those of conventional casting, the number of sulfides per unit area in 443MnS steel by ultrasonic vibration assisted casting is increased by 288 number/mm², the average length of sulfides is decreased by 33.8 μm, the average width of sulfides is decreased by 0.4 μm, and the aspect ratio of sulfides is decreased by 7.76.