Alsen is a city in Cavalier County, North Dakota, United States.

Alsen is located on State Route 66, approximately 8 miles (13 km) west of Loma.

25.0% of all households were made up of individuals, and 12.6% had someone living alone who was 65 years of age or older.

20.0% of all households were made up of individuals, and 12.0% had someone living alone who was 65 years of age or older.

There were 22.7% of families and 44.2% of the population living below the poverty line, including 70.6% of under eighteens and 28.6% of those over 64.

The former high school in Alsen, which closed due to low enrollment in 1980, recorded the longest basketball winning streak in North Dakota basketball history, at 79 games from 1956 to 1959.