A tetraploid cyprinid loach, Misgurnus anguillicaudatus was induced by applying heat shock. The efficiency of inductions changed with the time of initiation of treatment and the duration of treatment. The highest incidence of tetraploid was obtained at the treatment of $41^{circ}C$ for 3 min, 28 min after fertilization. Ploidy level was estimated by kariological examination and flow cytometric analysis. The tetraploid cyprinid loach had 4n = 100 chromosomes, while the diploid had 2n = 50. The erythrocytic volume of the tetraploid was 1.65 times larger than that of the diploid. The DNA content of the tetraploid and diploid showed 6.547 pg/cell and 3.067 pg/cell, respectively.