The morphology, motility and viability of frozen-thawed southern minke whale (Balaenoptera acutorostrata) spermatozoa was evaluated. The whales used in this study were captured during the period from December 1994 to February 1995 for the Japanese Whale Research Programme under Special Permit in the Antarctic. Each sperm sample recovered from the vasa deferentia of eleven whales was diluted to a 1:9 ratio with Tris (300 mM)-citrate (94.75 mM)-glucose (27.75 mM)-egg yolk (15%; v/v)-glycerol (5%; v/v) diluents. The diluted samples were cooled gradually at 5 C for 2 h, frozen at -80 C and kept in liquid nitrogen. After thawing, sperm motility was evaluated subjectively. Sperm viability was assessed by eosin-nigrosin staining. Sperm abnormality and head morphology were assessed by carbol-fuchsin staining using phase-contrast microscopy. Sperm dimensions were measured using a calibrated projection microscope. Sperm motility and viability respectively varied from 1.0 to 20% (7 out of 11 samples), and 1.0 to 11.6%. Sperm concentration ranged from 13 to 585.3 × 10⁶ spermatozoa/ml. The mean proportion of morphologically abnormal spermatozoa was 84.0 ± 6.7%. Seven morphotypes of sperm heads were observed, and the most common types were conical and elliptic in shape. The mean total length of spermatozoa was 56.7 ± 0.5 μm, with their sperm heads measuring 5.2 ± 0.1 μm for length and 3.0 ± 0.0 μm for width; the mean length of sperm tail was 51.7 ± 0.5 μm.