Kleven (Ukrainian: Клевень) is a 113 km (70 mi) long right tributary of the Seym in Russia and Ukraine. It drains a catchment area of 2660 km and has a gradient of 0.36 m/km.

Kleven rises in the south-west of the Central Russian Upland in the south of the Russian Bryansk Oblast near the M3/E101 trunk road and initially flows south. After a few kilometers, it comes across the Ukrainian village of Sopych. From there it forms the border between the Ukrainian Sumy Oblast and the Russian Kursk Oblast over a longer stretch, changing its direction of flow mainly to the southwest, until it finally flows into the Seym at the southern edge of the village of Kamin in Sumy Oblast.