The present experiment was conducted to study the effects of supplementation of Sesbania sesban on the milk yield of ewes and growth rate of their lambs. The experiment was done with animals that had been fed for 16 months on a basal diet of teff straw supplemented with concentrates alone (0% S. sesban) or 95% of supplementary protein provided by S. sesban (accession 15019). Thirty lactating ewes and their single lambs of Ethiopian highland Menz sheep were used in this study. The post partum weight of ewes and birth weight of their lambs ranged between 16¿22 kg and 1.3¿2.4 kg. The ewes continued to be fed a teff straw basal diet and supplemented with two levels of S. sesban (0, and 95% of supplementary protein provided by S. sesban and the rest being provided by concentrates) for 3 months. Three weeks after birth lambs were offered a succulent green grass¿legume mixture ad libitum. Dry matter and organic matter intake of basal feed and total feed, live weight at weaning and post partum daily body weight gain of ewes were not significantly different (P > 0.05) between treatments. The milk yield of ewes was significantly affected (P <0.05) by dietary treatments. Ewes supplemented with S. sesban showed a 13% increase in milk production over ewes supplemented with concentrates. The peak lactation for ewes supplemented with S. sesban was higher and persisted longer than for ewes supplemented with concentrates. Lambs born from ewes supplemented with S. sesban had a significantly higher pre-weaning growth rate and were heavier at weaning (P <0.05) than lambs born from ewes supplemented with concentrates. We concluded that supplementation of S. sesban at 30% of the ration (0.98% of their body weight) during lactation improved milk yield of ewes and growth rate of lambs.