Olsberg (Swiss German: Olschprg) is a municipality in the district of Rheinfelden in the canton of Aargau in Switzerland.

With some interruptions, the part of Olsberg to the right of the Violenbach stream belonged to the Austrian district of Rheinfelden from 1330 until 1797.

After 1797 it was a French protectorate and then went with the rest of the Fricktal to the newly formed Canton of Aargau in 1803.

The left hand side of the stream belonged to the city of Basel from 1461 and later to Canton of Basel-Country (and now forms part of the municipality of Arisdorf).

Of the rest of the land, 0.25 km2 (0.097 sq mi) or 5.4% is settled (buildings or roads), 0.01 km2 (2.5 acres) or 0.2% is either rivers or lakes.

[4] The municipality is located in the Rheinfelden district, in the lower Fricktal (Frick river valley).

[9] The age distribution, as of 2008[update], in Olsberg is; 23 children or 6.3% of the population are between 0 and 9 years old and 37 teenagers or 10.2% are between 10 and 19.

[11] About 76.7% of the total households were owner occupied, or in other words did not pay rent (though they may have a mortgage or a rent-to-own agreement).

[15] The historical population is given in the following table:[3][10] The former Cistercian convent, church and outbuildings are listed as a Swiss heritage site of national significance.

[9] From the 2000 census[update], 86 or 22.9% were Roman Catholic, while 166 or 44.3% belonged to the Swiss Reformed Church.

[18] The cellist Sol Gabetta has since 2005 organized a chamber music festival in Olsberg called Solsberg,.