A system and method capable of measuring the fat content in the target organ by the gray level distribution of pixels forming a ultrasonic section image and a recording medium of recording a fat content measuring program are disclosed. In order to quantify the fat content of the target organ from the information of the stored ultrasonic section image, a target section and a comparative section in each of the longitudinal sections are set, and a representative gray level value of the respective section is calculated, thereby the fat content of the target section is quantified in a numerical value relative to the representative gray level value of the comparative section.