A study was carried out at Mallawi Experiment Station, 300 km southern Cairo, in which 16 Chios (CC), 31 Ossimi (00) and 21 of their F1 crossbred ewes (50% Chios- 50% Ossimi, Co). The Co halfbred ewes were mated to CC rams to produce 75% Ossimi (3/401/40) lambs, whereas 00 and CC ewes were mated to rams of their breeds. The study included only ewes having single lambs in two lambing seasons; summer and winter. In the summer, total 8-wk milk yield (suckling period) averaged 128.9, 53.4 and 77.1 Kg in CC, 00 and the halfbred ewes, respectively (P<.01). Total milk yield averaged 201.6, 65.0 and 110.2 and days of lactation were 151.1, 79.6 and 106.7, respectively (P<.01). In the winter, total 8-wk milk yield averaged 138.6 (P<.01), 55.0 and 59.5 kg for CC, 00 and the halfbred ewes, respectively. Total yield averaged 209.1 (P<.01), 65.9 Kg and 76.5 kg and days of lactation were 153.3, 79.8 and 93.4, respectively (P<.01). At weaning (2 mo of age), CC and 3/4C1/40 lambs weighed significantly heavier than 00 lambs; 12.58, 12.83 and 11.43 Kg, respectively. In conclusion, when co halfbred ewes were mated to CC rams, milk production of the ewes and preweaning gains of their 3/401/40 lambs were increased compared to pure 00 ewes and their lambs.