To determine the distribution of feline blood types and then to estimate the risk of neonatal isoerythrolysis (NI) in non-pedigree cats, we typed blood of 482 cats of both genders and various breeds (336 domestic shorthair cat and 146 pedigree) from August 2005 through July 2007. Blood samples from Seoul and Kangwon province were typed within 5 days after collection by the simple tube method. High-titer anti-A antiserum and anti-B reagent, prepared with Triticum vulgaris lectin, were used to determine type A and type B blood, respectively. The majority of cats were type A (n = 465, 96.5%) and only 3.5% (n = 17) were type B. No type AB blood were detected. Blood type distributions among the non-pedigree and pedigree cats were similar: for non-pedigree cats, 96.4% were type A and 3.6% were type B, whereas for pedigree cats, 96.6% were type A and 3.4% were type B. All type B cats had a very strong agglutination reaction to anti-A antiserum: 8 sample for 3+ and 9 for 4+. Assuming 19% of estimated frequency for the type-B allele in domestic cats, the calculated proportion of random mating from this population at risk for developing NI was 3.4%. Based on this finding, it is strongly recommended that blood typing be performed prior to any blood transfusion or breeding to minimize blood type incompatibilities. Further comprehensive studies on the titer of naturally occurring antibodies in cat populations in Korea and the prevalence of possible NI in practice are clearly required.