Genetic tends in three lamb weight traits (at 60, 120 and 180 days of age) were studied on a total of 10,241 Rahmani and 6365 Ossimi lambs, progeny of 319 and 235 sires, respectively, over a 30-year period (1970–1999). Mixed model methodology based on a multi-trait animal model was used. Genetic trends were estimated by regressing estimated breeding values on year of birth. Genetic trends were positive and highly significant for all traits in both breeds for lamb weights at 60, 120 and 180 days of age being 38, 92 and 135 g per year in Rahmani ( P<0.0001) and 20, 21 and 21 g per year in Ossimi ( P<0.0001), respectively. Estimates of heritability obtained for the three weights using a multi-trait animal model were 0.18, 0.28 and 0.46 in Rahmani and 0.67, 0.24 and 0.23 in Ossimi.