This study was conducted to find out the actual conditions of breeding difficulties occurrence of cows which cause big trouble on rational dairy farming in Korea and also to obtain basic data for removal plans of these diseases. Research survey was carried out for two years from January, 1966 to December, 1967 with 1,041 dairy cows. The results obtained in this study is summarized as follows: 1. Distribution of cows by age group. There were 2-6 years old cows in abundance by 87% of all cows, and the 3 years of age cow group occupied the largest part by 28.5% of total number. This showed that farmers had an advantage of cows age in feeding cows. 2. Distribution of cows by calving order group. Calving orders of the cows showed that 33.2% of them was from first calving and 3.0, 3.7% from above-5, 6 th calving orders. 3. Conception condition of cows. Conception condition of cows by mating times showed that 47.9% of the cows was conceived at the first mating and 84.1% at the third mating. Repart breeders amounted to 15.9% of the cows. 4. Occurrence of breeding difficulties. The percentage of infertile cows was 31.3%. The diseases taken before conception (ovarian disorder, uterine and vagina diseases) amounted to 15.1% and the diseases taken after conception (abortion, stillbirth, difficult delivery and stagnation of afterbirth etc.) amounted to 16.2%. 5. Relationship between diseases and ages of infertility cows. Ovarian disorder was found in abundance by 26.6% on old age cows (above 7 years old), and the complication (ovarian and uterine disease) by 27.2% on 6 years old cow. Consequently, these diseases had a tendency to be found in old age cows, although, they were found at all ages. 6. Relationship between breeding difficulties and nutrition. Nutritional condition of infertile cows was poor. The percentage of under-nourished cows of infertile cows was 47.4%. Undernourished cows appeared in the case of ovarian disorder by 34.5%, by 61.1% in the complication and by 61.4% in the uterine disease. Supernutrition was found by 10.5% in ovarian disordered cow. 7. Relationship between breeding difficulties and feeding. Feeding condition o these cows showed that cows fed with poor nutrient (T.D.N.) and medium level of protein (D.C.P.) occupied the largest part of them by 42.8%, poor nutrient and low level of protein by 22.6%, poor nutrient and high level of protein by 11.9% and rational condition, medium level of T.D.N. and D.C.P., by only 2.4%. 8. Relationship between breeding difficulties and milk yields. Cows producing above 5,000㎏ of milk per year were found by 52.4% in the group with breeding difficulties and 33.3% in normal group. Four high milk producers producing more than 7,000㎏ per year were found in the disease group. However, there was no such high milking cow in normal group. So it seemed that the more milk a cow produced the more occurrence of breeding difficulties were found.