The chromosome morphological structure, size and number were studied by early embryos of chicks. The chromosomes of 100 early embryos which were derived from a pure line of Single Comb White Leghorn, White Cornish, and crossbreds of these breeds were examined. In the results, the total number of chromosomes appeared to be 72-78. But the modal number for the diploid chromosome was at least 78. These chromosomes were consist of 6 pairs of macrochromosomes, 32 pairs of microchromosomes and ZW or ZZ sex chromosomes. In addition the chromosome size and shape were studied by the centromeric index and relative length of pure breeds and crossbreds. The differences of morphological figures were not significant in centromeric index and relative length. Instead, this pattern was very similar among breeds except that the one individual of the cross between Leghorn (♂) and Cornish (♀) produced triploid embryos. The gonosomic complement was ZWW. The results of the present investigation of chromosome pairs were as follows. 1. Pair 1 and 2; metacentric and submetacentric chromosomes which could be clearly distinguished from each other by size. 2. Pair 3 and 4; acrocentric chromosomes of similar length but the 4th pair had a distinct short arm which was not present in the 3rd. 3. Pair 5; metacentric sex chromosomes. Z chromosome had relative 5th length but the W chromosome had slightly shorter length than 7th pair of chromosomes. 4. Pair 6; acrocentric chromosomes similar in shape to pair 3 but of little more than half the size. 5. Pair 7 and 8; acrocentric chromosomes, but the 7th pairs had a definite short arm. 6. Pair 9; similar length to the 7, 8 pairs but had a medially placed centromere. 7. Microchromosomes of 30 pairs; nearly all acrocentric chromosomes which appeared as paired dots.