Abstract: A study was carried out on the chromosomes of periodic Brugia walayi usirg air drying preparations of testis, ovary and uterus. The results showed that the oogonial metaphase consisted of 4 pairs of small-sized autosomes and one pair of large-sized rex-chromosomes, that the spermatogonial metaphase consisted of 4 peirs of small-sized autcmes and one large-sized and one medium-sized sex-chromosome, the oocytes at diakinesis had 5 bivalents, the secondary spermatocytes 5 wnivalents and the fertilized eggs 10 chromosomes. The above-mentioned findings revealed that the chromosome number was 2n=10 and that the sex-determining mechanism was of the XY-XX type in this type of B. malayi.