Gunnekleivfjorden is a fjord in Porsgrunn Municipality in Telemark county, Norway. The 2-kilometre (1.2 mi) long fjord is located at the head of Frierfjord in the town of Porsgrunn.

The west side of the fjord is defined by the Herøya peninsula at the mouth of Telemarksvassdraget. Herøya features a large industrial park that was founded in 1928. It contains major facilities of Norsk Hydro, Yara, and REC (ScanWafer subsidiary). The east side of the fjord belongs to Skrapeklev, a residential area in the town of Porsgrunn.

The fjord's mouth lies on the north end of the fjord where the Porsgrunn River discharges into the Frierfjord at Norsk Hydro's factory complex. The Skien River, which begins in Skien, is called the Porsgrunn River as it runs through Porsgrunn. Small watercraft traffic can also pass through a man-made canal at the south of the fjord.

The fjord is heavily polluted due to the development of the industrial area at Herøya. The fjord has brackish water with a significant amount of fish (both freshwater and saltwater species).

• List of Norwegian fjords