Sea hares are a group of marine molluscs which possess many ways for defense including the chemical defense. The hares produce ink fluid from the ink gland to escape and protect themselves from their enemies. The ink gland of sea hares secrete, the ink fluid which contains many bioactive factors acting against potential enemies with toxic activities. Aplysia dactylomela is a large sea hares exhibit shallow water, collected from Qusair City, Red Sea, Egypt. Few cases of human intoxication following ingestion of sea hares were reported. In the present investigation, the lethality of the ink fluid toxin was determined (LD50 = 93.234 mg protein/Kg via i.p.) in mice. The effect of ink fluid on the ultrastructure of liver and kidney tubular cells were studied since, they are the potential organs for storing of most toxic agents entering the body. To examine these effects, an animal model formed of 24 mice was established. The animals were divided into four groups:, control, Group (1) and treated groups (2, 3 & 4) injected intraperitonealy with a sub lethal dose (58.45 mg protein/ ml) of the crude dialyzed ink fluid of A. dactylomela for each mouse and dissected after one, four, and 7 days respectively. Liver and kidney specimens were collected from animals of all groups at the expected time. The specimens were evaluated for ultrastructural changes by transmission electron microscope (TEM). Histologically, manifestations of degeneration were marked in the hepatocytes by cytoplasmic vacuolation, chromatinolysis, and hypertrophy and dilated RER. While, manifestations of apoptosis in the kidney tubular cells were marked by shrunken cells, loss of apical microvilli, basal and lateral enfolding, dense and heterochromatic nuclei, electron dense cytoplasm overcrowded with cytoplasmic organelles especially mitochondria and apoptotic bodies which appeared as engulfed membrane bounded bodies inside the normal neighboring cells from the start of the experiment. However, apoptotic manifestations appeared in the liver after 7 days of the injected ink. The administration of ink fluid of A. dactylomela produces serious destructive effects on the liver and kidney. This study sends a warning that this group are toxic and may caused some healthy problems for divers and researchers. The clinical ramifications of these observations mandate further studies.