Osbysjön, Freshwater lake in Osby Municipality, Sweden.

Osbysjön is a lake in Osby Municipality in Skåne, 4.86 square kilometres in area, 6 metres deep and 71 metres above sea level, drained by Helge å, which crosses its southern part. The peninsula Näset divides it into two halves; the northern part receives the small Driveån at the town of Osby. Its shores are mostly forest.

Osbysjön lies in the Helge å main catchment area and is fed by Helge å itself and the smaller Driveån. Kiselgur (diatomite) was mined on the peninsula Näset and on the islands Holmön and Viön; during the Second World War the diatomite from the islands was carried to Hasslaröd by barge. Barges also moved the Näset material, later by cableway to the Hasslaröd factory, which ran until 1951.

Näset, the peninsula that splits the lake in two, is a municipal nature reserve with walking trails and a birdwatching tower. Kiselgur (diatomite) was once dug here: the pits are now water-filled, and the material was carried off by 13 barges and then by cableway to the factory at Hasslaröd, which ran until 1951. Between 1928 and 1938 a barge-like motorboat ran a regular service from Osby town via Näset and Kvinnön to the Lövsta bathing place.

The lake has several access points around its perimeter where visitors can easily reach the water and set up for activities. The best time to visit is spring through fall when weather conditions are mild and recreational opportunities are most available.

On the peninsula Näset, which splits the lake in two, water-filled pits remain from kiselgur (diatomite) quarrying. The material was carried ashore by 13 barges and then by cableway to the factory at Hasslaröd, in operation until 1951; afterwards it went by lorry to Skånska Kiselgur's plant in Östra Genastorp. A birdwatching tower and walking trails now stand on the reserve.