The data set used in this study contained 8793 records of lamb's LONGEVITY (days) from 320 sires and 2349 dams collected during 1989 to 2014, from the Lori-Bakhtiari flock at Shooli station in Shahrekord, Iran. Genetic parameters (partitioned into autosomal, sex-linked and maternal) and breeding values of cumulative lamb's LONGEVITY from birth up to yearling age (at 1, 2, 3, 6, 9 and 12 months) were estimated using re-stricted maximum likelihood procedure. The results showed that the overall mean of the cumulative longev-ity of lamb up to yearling (12 months of age) was 295.87 days. The effect of fixed factors; year and month of birth, sex of lamb, age of dam, lamb birth weight as quadratic covariate and dam body weight as linear covariate were significant (P<0.05) on lamb's LONGEVITY. The heritability estimates of lamb's LONGEVITY were low and ranged from 0.01 to 0.08 for autosomal, 0.01 for sex-linked and 0.02 to 0.03 for maternal additive genetic effects. The estimates of autosomal, sex-linked and maternal genetic correlations of lamb's longev-ity in different ages were high. The pearson and spearman correlation coefficients between autosomal breeding values and sex-linked breeding values in lamb's LONGEVITY at different ages were 0.15 to 0.46 and 0.11 to 0.43 respectively. Thus, lamb's LONGEVITY up to yearling can be improved by farm management prac-tices and improving environmental factors at first. Genetic analysis using linear models which able to esti-mate breeding values in direct (autosomal and sex-linked chromosomes separately) and maternal effects, could be more effective to improve LONGEVITY in lambs.