Which organ is responsible for defecation?

Defecation is the process of eliminating undigested and unabsorbed food material from the body in the form of feces. 

After the absorption of water and nutrients in the small intestine, the undigested and unabsorbed food material passes into the large intestine. The large intestine absorbs more water and electrolytes from the fecal matter and helps in the formation of solid feces. The feces are then eliminated from the body through the rectum and anus in the process of defecation.

Therefore, the large intestine is responsible for defecation.