In order to determine the sex of preimplantation embryos prior to transfer in cattle, a series of experiments were carried out using 45 Holstein donor cows to examine the ovarian response on the gonadotropin and PGF2${alpha}$, and the morphology of fresh embryos or frozen/thawed embryos after deep freezing at -196$^{circ}C$. The sexing of embryos treated with the medium containing H-Y antiserum(10%, v/v) and FITC anti-mouse IgG(10%, v/v) were analysed by chromosomal analysis, and the sex of the embryos which survived were ascertain after delivering the pups. The results obtained were summarized as follows ; 1. The average number of developed follicle and corpus luteum per cow were 13.5 and 8.1, and the ovalation rate was 60.1%. 2. Of 220-ova recovered, 75(34.1%) were morula and 91(41.4%) were blastocyst, and the morphological normal and abnormal rate of ova recovered were 75.5% and 24.5%, respectively. 3. Of 39 frozen/thawed embryos, the scores of normal morula and blastocyst, after thawing were 79.2%(19/24) and 73.3%(11/15). The average rate of frozen/thawed embryos which appeared morphologically normal post thawing was 76.9%(30/39). 4. The sex ratio was measured using the embryos treated with immunofluorescence assay to examine the relationship between embryo developmental stage, sex ratio of morula stage embryo was 42.2%(19/45) fluorescing and 57.8%(26/45) non-fluorescing, on the other hand, the ratio switched to 46.8%(29/62) fluorescing and 53.2%(33/62) non-fluorescing embryo in blastocyst stage. The sex ratio was also measured between fresh and frozen/thawed embryos, fresh and frozen/thawed treated embryos were indicated 45.8%(38/83) fluorescing, 54.2%(45/83) non-fluorescing and 41.7%(10/24) fluorescing, 58.3%(14/24) non-fluorescing. This trend indicated the approximal sex ratio was 1 : 1. 5. The result of karyotype test showed the successful rate of sexing embryo is fluorescing and non-fluorescing was 21.2%(7/33) and 29.6%(8/27). The female to male ratio within 33 fluorescing was 28.6 : 71.4, and the ratio of 27 non-fluorescing embryos was 87.7 : 12.5. 6. Of the embryo transferred after assignment of H-Y phenotype, five of the fluorescing embryos survived to term, all was males. Whereas six non-fluorescing embryos also survived to term and the sexes of the calves were 1 male 5 female.