Summary: Horses require, as do all mammals, sufficient sleep in order to maintain their physical and psychological performance.The aim of the present study was to clarify whether different bedding material in free-stall housing and box stall housing show significant influences on the lying behaviour of horses. The influence of the housing system was investigated as well. The bedding material used was wheat straw, wood shavings and straw pellets. In the course of one year the lying behaviour of six Hanoverian mares aged 2 years was recorded by means of ALT (activity, lying time, temperature) pedometers and video recordings (continuous sampling). At the same time three horses were housed in a free-stall housing system (box with adjacent pen) and three horses in closed single boxes. The total recumbency time, sternal recumbency, lateral recumbency, the number of lying occurrences, as well as the usage of the partly available pen were examined at night (18:00 -06:00). When considering the total recumbency time in the box (without consideration of the housing system) a significantly longer recumbency time was detected when using wood shavings (211.56 ± 69.87 min/night) in comparison to straw pellets (177.34 ± 98.87 min/night). On wheat straw the total recumbency time in the box was 200.92 ± 86.32 min/night. When considering the housing systems (without taking the bedding materials into account) 100 % of the recumbency time in the box stall housing system occurred in the box, inevitably due to the experimental set-up (235.56 ± 55.82 min/night). In the free-stall housing sysem the total recumbency time in the box and pen was significantly lower with 204.44 ± 63.43 min/night (recumbency time in the box: 158.00 ± 94.62 min/night; 77 %). The recumbency time varied depending on the bedding material as well as the housing system. On the various bedding materials (wheat straw: 243.77 ± 50.08min/night; wood shavings: 233.02 ± 58.92 min/night; straw pellets: 229.67 ± 57.99 min/night) the total recumbency time in the box stall housing system showed no significant differences. In the free-stall housing system in comparison the total recumbency time for each bedding material (wheat straw: 157.48 ± 93.64 min/night; wood shavings: 190.7 ± 73.67 min/night; straw pellets: 126.46 ±104.01 min/night) was significantly lower than in the box stall housing system. In comparison with the other bedding materials the wood shavings in the free-stall housing system partly showed a significantly longer recumbency time in the box. The use of straw pellets resulted in a longer recumbency time and a higher number of lying occurrences in the pen (free-stall housing system) in comparison to wood shavings and wheat straw. In conclusion, horses kept in single boxes with adjacent sandy pen, prefer wheat straw or wood shavings in the box as opposed to straw pellets. The total recumbency time of horses housed in box stall housing was longer on all bedding materials than in free-stall housing. However, none of the used bedding materials shortened or length...