This study was aimed to search testis growth of Karakal male lambs raised in intensive conditions and to build the forecasting model of live weight in lambs using 4 data mining CHAID, Exhaustive CHAID, CART, and multivariate adaptive regression splines (MARS). Effects of genotype and some environment factors such as birth type, dam age, lamb' age in control and live weight on testis characteristics were also researched. The furthest importance sequence was obtained for testis length (TESLENG) (100%), followed by age, testis diameter (TDIA), age in control (DAGE), birth weight (BW), around scrotum (SCC), scrotum length (SCL) and birth type (BT). TDIA 4.5 and TESLENG 9 will provide 4.095 to LW. Analytic results shown that MARS outperformed CHAID, Exhaustive CHAID, and CART approaches in terms of R-2, Adj. R-2, RMSE, SD ratio, MAPE and AIC provided effective alternatives for forecasting live weight of lambs. Purpose of MARS algorithm having very high predictive precision in the prediction of LW from body features may onward a new view for 39 lambs breeders.