The Syrian Observatory for Human Rights said at least 412 people, including 219 IS jihadists, 173 Kurdish fighters and affiliated forces and 20 civilians, had been killed since September 16.
The group said it believed the real toll was much higher, but that it was difficult to document deaths in the clashes because of secrecy by fighters and the inaccessibility of much of the area.
IS jihadists began advancing on Kobane three weeks ago, quickly seizing a string of villages around the town, which is also known as Ain al-Arab.