The objective of this study was to investigate the effect of rumen-protected L-arginine (ARG) on the udder of ewes and growth rate of newly born lambs. At 15±3 days postpartum, ten clinically healthy, 3-4 years ewes with body weight 49.11±4.03 Kg were divided randomly into 2 equal groups Group 1: served as control, without any treatment. Group 2: treated with Rumen protected L-Arginine 20 Mg/Kg body weight, for 30 days. The animals were examined with ultrasound, and blood samples were taken at the 10^th, 20^th and 30^th days of ARG supplementations begin, and the lambs were weighted in the same times. The results of this study revealed that significant differences (P<0.05), between ARG treatment and control one, in some udder measurement's.The glucose concentration after 10, 20, and 30 days of treatment showed significant differences (P<0.01, and 0.05), where the ARG treatment had higher glucose concentration than control. Also, there were significant differences (P<0.05), between ARG treatment and control group, in the urea and AST concentrations.There was an increase in the lamb's body weight at 10^th, 20^th and 30^th Day of ARG treatment. The ARG supplementation appeared to have significant effects on postpartum udder measurements as well as the growth rate of the newly born lambs.