Seventy purebred and crossbred lambs were used in this study to investigate the effect of some factors affecting growth traits, daily gains and survival rates of lambs under unlimited suckling regime. Ewes in the flock were not milked and lambs were subjected to unlimited suckling regime without weaning. Results showed that, variation among breed groups were significant (P<0.01) in birth, 6, 9 months and yearling weights, as well as, at 3^rd months was a significant (P<0.05). Male born lambs were significantly heavier (P<0.01) than females except at 3^rd months. Type of birth or the ages of dam have no significant effect on body weights in all ages except at birth, where it was significant. Breed of lambs have a significant effect on the average daily gains, while there was no significant effect of sex, type of birth or age of dam, except at the period from 3^rd to 6^th months. The superiority of crossbreed lambs over their parental breeds from birth to yearling age ranged between 2.18 and 1.65 % from birth to yearling. Likewise, the daily gain of crossbred lamb groups during the four periods studied, have the same results. Breed of lambs have a significant effect (P<0.05) on the survival rate of lambs, since the survival rate of Rahmani lambs was higher at the early stages of life while the crossbred lambs showed superiority in survival rate with advancing age. Sex did not have any significant effect on the survival rate, except at birth. Type of birth and the age of ewes had a highly significant effect on survival rates in all periods studied except at the age of a year. It is concluded that Chios breed could be an appropriate breed for terminal sire crossbreeding to improve both Rahmani ewe's productivity and early lamb growth under Upper Egypt conditions system.