Tjongsfjorden is a fjord in the municipality of Rødøy in Nordland county, Norway. The long fjord begins just west of the Svartisen glacier and flows west and flows into the Rødøyfjorden, just east of the island of Rødøya. The mountain Blokktinden lies on the southern shore of the fjord. The villages of Tjong and Vågaholmen lie along the northern shore of the fjord. Norwegian County Road 17 runs along the inner part of the fjord.