This experiment was conducted to demonstrate the degree of seed abortion and germination percentage in seeds derived from interploid crosses between diploid and tetraploid grape cultivars as the first step for triploid breeding. In the crosses between three diploid and six tetraploid grape cultivars, a total of 11,015 pollens was pollinated and percentage of seed set was 21.7% on average. In the crosses between five tetraploid and twelve diploid grape cultivars, a total of 9,107 pollens were pollinated and percentage of seed set was 9.0% on average. In 2x × 4x and 4x × 2x crosses, the frequency of sinker seeds reflecting the presence of embryo and endosperm was 71.2 (2,551 seeds) and 58.7% (603 seeds), respectively. The sinker seeds derived from 2x × 4x and 4x × 2x crosses were treated with low temperature, and then were sowed for determining germination rates. In 2x and 4x crosses, 194 seeds were germinated and the percentage of seed germination was 7.6% on average. In 4x and 2x crosses, 77 seeds were germinated and the percentage of seed germination was 12.8% on average. The percentages of seed germination were not different between the 4x × 2x and 2x × 4x crosses. Chromosome number observation in root tip cells indicated that all seedlings obtained from 2x × 4x and 4x × 2x crosses were triploid plants with 57 chromosomes. In the 2x × 4x and 4x × 2x crosses, most seeds derived from crosses did not have perfectly developed endosperm. Although frequency of seed with embryo in interploid crosses was high, cause of low germination percentage was judged by the result of regeneration of embryo.