To investigate the possibility of using ultrasound to estimate carcass composition, 38 Moghani male lambs were made use of. Subcutaneous fat depth (USFT) and longissimus dorsi muscle depth (ULMD) and area (ULMA) were assessed in the site between 12th and 13th ribs by using ultrasound equipped with an 8 MHz probe. The lambs were then slaughtered. Carcasses were cold stored at 4°C for 24 hours and then the corresponding measurements performed on the carcasse. The right half of each carcass was dissected to determine carcass composition including muscle, fat and bone. The results revealed that correlation coefficients between the measurements of USFT, ULMD and ULMA and the corresponding carcass recordings were 0.51, 0.71 and 0.92, respectively. Also the correlation coefficients between ULMA and the levels of muscle and bone were recorded as 0.33 and 0.48, respectively. Coefficient of determination in simple regression equation to estimate the hot carcass weight, cold carcass weight, carcass weight without fat-tail and subcutaneous fat depth as based on body weight were 0.85, 0.87, 0.77 and 0.13, respectively. Multiple regression models while using USFT, ULMD, and ULMA in addition to body weight promoted the R2 to 0.86, 0.88, 0.83 and 0.53, respectively. Also the coefficient of determination in simple regression equation to estimate carcass longissimus dorsi muscle area employing only ULMA and carcass longissimus dorsi muscle depth with an employment of only ULMD were recorded 0.86 and 0.50, respectively. The results show that the use of ultrasound to estimate carcass composition on live sheep can be done successfully. Therefore important traits can be asessed and made use of in breeding programs without the need to slaughter killing the animal.