古尔德堡海峡是丹麦的海峡，位于该国东南部波罗的海，将西面的洛兰岛和东面的法尔斯特岛相隔，南接梅克伦堡湾，长约20公里。

For the Danish municipality, see: Guldborgsund Municipality.

Guldborgsund is the strait between the Danish islands of Lolland and Falster. It connects Smålandsfarvandet in the north with the Bay of Mecklenburg in the south. It is navigable for craft of up to 6 metres draught in its northern part and is used for commercial traffic to Nykøbing Falster. The southern part is much shallower with a minimum depth of approximately 2 metres, and can only be used by yachts and other small craft.