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The phenotypic and genetic characteristics of growth traits in Lori-Bakhtiari lambs were studied using multitrait animal model analysis along with a DFREML procedure. Ggrowth trait records of 4889 lambs, collected during the period of 1989 to 2002 in Sholi Station, ShahreKord were used as data. Analyzed traits were weight at birth, weight at 1, 3, 6, 9 and 12 months of age, average daily gains from birth to 1-month, 1 to 3-months, birth to 3-months, 3 to 6- months, 6 to 9-months, 9 to 12-months, and Kleiber ratio (average daily gain to weaning/weaning weight 0.75 The ovarall mean (s.d) of body weight traits were 4.9 (0.8), 12.1 (2.5), 27.5 (5.5), 40.2 (8.0), 52.0 (8.5) and 56.8 (10.3) kg respectively; for average daily gain traits, they were 233.9 (62.7), 257.7 (66.3), 250.5 (56.3), 137.9 (56.8), 129.1 (43.1) and 63.2 (43.6) gr respectively while for Kleiber ratio it was 20.8 (2.1). Birth weight exhibited the highest estimate of direct heritability (0.30 + 0.04), 1-month body weight had the lowest estimate (0.13 + 0.03), and thereafter steadily increasing up to 12-months of age. The highest maternal heritability was estimated for birth weight (0.16 + 0.03) and thereafter decreased with increase in the age of lambs. The direct genetic and phenotypic correlations among body weight traits ranged from 0.62 + 0.09 to 0.98 + 0.02, from low to hgigh respectively. The highest and lowest direct heritability of average daily gain traits were estimated for birth to 1-month (0.38 + 0.04) and 3 to 6-months of age (0.09 + 0.03), respectively. Genetic correlations among average daily gains in preweaning traits were high and positive, while genetic correlations among average daily gains before 3 months with average daily gain from 3 to 6-months of age were low with other genetic correlations being moderate and positive. The direct and maternal heritability for Kleiber ratios were 0.08 + 0.02 and 0.13 + 0.02, respectively. The estimate for genetic correlations between Kleiber ratio and birth weight, average daily gain up to weaning as well as weaning weights were 0.31 + 0.14, 0.80 + 0.06 and 0.73 + 0.08 respectively.