The aim of the study was to compare the milk yield in ewes from Bulgarian Dairy Synthetic Population and their crosses with Lacaune. “Blood introduction” of Lacaune breed with F1 cross ram was carried out on 40 purebreed ewes of Bulgarian Dairy Synthetic Population (BDSP). The ewes were equal in the sequence of lactation, genealogic line and milk yield. The object of the present study were 32 ewes on first lactation – purebred BDSP (n=16) and crosses of the breed with Lacaune (n=16). The ewes were reared in the experimental farm of the Institute of Animal Science- Kostinbrod, Bulgaria. The milk yield for the control day was determined after the AC method of ICAR as the standard 120 d milking milk yield was determined. The fertility was determined as a ratio of the number of the lambs born alive to the number of the experimental ewes. The content of fat, total protein, dry fat-free residue and dry matter were measured in each control of 20 ml of individual sample for each of the animals, using milk analyser Ecomilk, Bultech. The data were evaluated through the Data Analysis statistical package of Excel 2016, Microsoft. The effect of the crossbreeding on the examined traits was assessed through one way ANOVA. No effect of the “blood introduction” from Lacaune was observed on the milk yield and fertility of the ewes. No significant difference between the mean milk yield for a standard 120 period of first lactation was found (79.47 l and 81.83 l, respectively for the purebred ewes and the crosses).  The percentage of the fat and the dry matter of the first control in the Lacaune crosses (5.27% and 16.64%) was significantly lower (P<0.01; P<0.05) when compared to the purebred BDSP ewes (6.21% and 17.32%).