Octopus variabilis has become one of the most popular seafood for its delicious taste,which has large market demand in China and is advantaged in marine products exports.However,due to the over fishing and water pollution,the natural resource of Octopus variabilis declined rapidly.For this reason,the industry of artificial culturing got rapid development.The Octopus variabilis will spurt the ink when meeting the stimulation originally.The peculiar ink defence system of Octopus variabilis is based on the activity of the highly specialized ink gland which is deputed to the continuous production of the black insoluble melanin pigment that is stored in the ink sac.This organ has been studied in other cephalopod,but the ink gland in Octopus variabilis is different from the others.Therefore,the histology of the ink sac and ultrastructural structure of the ink gland of Octopus variabilis was studied using light microscopy and electron microscopy in this paper.The observed results showed that the ink sac was composed of ink sac body,pipe and ink glands.The ink sac of Octopus variabilis opened into the end of the recta near the anus by pipe.The wall of the ink sac and pipe were both composed of epicardial,muscular layer,submucosa layer and mucosa layer.And the epicardial of ink sac wall were stratified squamous epithelium.The ink glands concentrated at the bottom of the ink sac,were formed by the hyperplasia of the mucasa epithelium to the cavity of the ink sac,shaped as rope with abundant connective tissue in the centre,there was cavity between branch of ink gland; Type A cells which can not secrete melanin and type B cells which can secrete melanin were observed.Microvillus were located in apex of the type B cells,and the ink particles adhered to the rough endoplasmic reticulum were formed in the melainin vesicles.The vesicles were released with exocytosit and cell disruption finally.