Kase Run is a tributary of Mahoning Creek in Montour County, Pennsylvania, in the United States.

The stream and a number of its tributaries are considered by the Pennsylvania Department of Environmental Protection to be impaired by siltation due to agriculture.

Kase Run begins in a small pond immediately south of Styer Road in eastern West Hemlock Township.

[2] Kase Run joins Mahoning Creek 4.70 miles (7.56 km) upstream of its mouth.

[3] The water temperature of Kase Run has been described as "not particularly warm or cold" by A. Joseph Armstrong in his book Trout Unlimited's Guide to Pennsylvania Limestone Streams.

[4] Kase Run is considered by the Pennsylvania Department of Environmental Protection to be impaired for its entire length except for its upper reaches.

[5] In 2010, at various points in the watershed of Kase Run, the runoff curve numbers ranged from 58.9 to 62.4, with an average of 61.3.

[6] The lower reaches of Kase Run lie over rock of the Wills Creek Formation.

The stream's southern tributaries are on rock of the Bloomsburg and Mifflintown Formation and the Clinton Group.

[11] In January 2007, 190 gallons of heating oil were spilled at a private residence and eventually contaminated a tributary of Kase Run.

As a result of the spill, the Pennsylvania Department of Environmental Protection issued an $8500 fine to the Leighow Oil Company.

[9] The Montour County Natural Areas Inventory has recommended planting native trees on Kase Run.