Abstract. The present study investigated effects of three semen extenders and storage temperatures on post-thaw characteristics of Bryde's whale spermatozoa. Spermatozoa were collected from the vasa deferens of three mature Bryde's whales captured during the Japanese whale research in the north-west Pacific (May to August 2007) after death. The three semen extenders used for freezing were 1) a commercialized synthetic extender (AndroMed: AM), 2) Trisbased + 10% bovine serum albumin (BSA) and 3) Tris-based + egg yolk (EY). The sperm samples from the three whales were frozen with the three extenders, and the post-thaw spermatozoa were stored at three different temperatures (35 C; 20-25 C, room temperature; and 5 C) for 0, 6, 12, 24, 48 and 96 h. At each time-point, total and progressive motility (PM), viability (live or dead), the hypo-osmotic test, defective acrosomes and malformation were examined. Immediately after thawing, AM resulted in similar recovery rates (60.4 and 83.3%) in 2 of the 3 whales examined and had comparable post-thaw recovery rates to those obtained using the EY and BSA extenders. Immediately after thawing, the proportion of PM in EY (17.6%) was higher (P<0.05) than that in BSA (15.0%). In the hypo-osmotic test, the proportions of AM (26.0%) and BSA (25.2%) were higher (P<0.05) than that of EY (17.3 %). The three extenders had similar viabilities (36.7, 37.9 and 32.1%, respectively), but the viability of BSA was higher (P<0.05) than that of EY. The present study showed that a synthetic semen extender, AndroMed, could be used for cryopreservation of whale spermatozoa in addition to Tris-based extenders containing bovine serum albumin or egg yolk. Storage of the post-thaw Bryde's whale spermatozoa was better at 5 C than at room temperature or 35 C. The frozen-thawed Bryde's whale spermatozoa maintained their motility and viability for at least two days at room temperature and for four days at 5 C. [5] used Bryde's (Balaenoptera edeni) whale spermatozoa freshly-diluted with m-PBS and stored at 4 C for in vitro fertillization (IVF) in the field. However, it has not been demonstrated yet how long the viability of frozen-thawed spermatozoa is maintained and what the most appropriate temperature is for post-thaw storage in baleen whales, including Bryde's whales. For domestic animals including sheep, post-thaw semen is usually maintained at 37 C for examinations of their motility and viability, but the body temperatures (35.5 to 37 C) of dolphins and whales are lower than those of other mammals, and no one has measured the body temperatures of live baleen whales, including Antarctic minke and Bryde's whales.There has been recent movement to eliminate all animal ingredients, such as egg yolk, milk and even bovine serum albumin (BSA), from semen extenders. Our recent studies [6-8] on artificial insemination (AI) in sheep have clearly shown that a soybean-based semen extender (AndroMed) is useful and comparable to the conventional semen extenders containing egg yolk or BSA. Fukui et al. [6] compared ...