Järvsöklacken, Nature reserve in Ljusdals kommun, Sweden.

Järvsöklacken is a 390.3-metre mountain and municipal nature reserve on the east side of the Ljusnan river, about five kilometres northeast of Järvsö in Ljusdals kommun. Its steep, shoe-shaped profile rises sharply above the valley. The 83-hectare reserve, created in 2011, holds old spruce forest rich in hanging lichens, rocky outcrops with heath flora and herb-rich broadleaf woodland.

Ljusdals kommun established the Järvsöklacken nature reserve on 5 October 2011. The 83-hectare protected area covers the mountain's forested slopes, where steep terrain has produced varied woodland. The reserve is managed by the municipality.

The mountain's characteristic shape, likened to a shoe heel, makes it a recognisable landmark across the Ljusnan valley. Hikers often start from the Hälsingegården farm in Kåsjö, on the east bank opposite Järvsö, about 4 km from the summit, or from the village of Klacken in the valley between Klacksberget and Järvsöklacken.

The reserve can be reached through multiple walking routes, with one main path taking around 4 kilometers to traverse. Sturdy footwear is recommended due to the steep inclines and uneven forest floor throughout the area.

The reserve's old spruce forest is rich in hanging lichens, and surveys there recorded 8 red-listed species and 21 signal species. The steep terrain also produces both bare rock with rock-dwelling flora and herb-rich broadleaf woodland within the 83 hectares.