The karyotype of chromosomes obtained from the germ cells of Paragonimus siamensis was analyzed by air-drying technique. The result revealed the diploid number of chromosomes to be 2n=22. The entire chromosomes consisted of one large-sized metacentric, four medium-sized subtelocentrics, three small-sized metacentrics or submetacentrics and three small-sized submeta-centrics or subtelecentrics. The relative arm lengths of the chromosomes were 20.13+/-1.21, 13.16+/-0.42, 11.07+/-0.48, 10.37+/-0.84, 9.29+/-0.52, 6.50+/-0.39, 6.42+/-0.34, 6.27+/-0.28, 6.04+/-0.58, 5.65+/-0.39 and 5.03+/-0.40% respectively. These data were comparable with those of other related species.