The study describes a ground contact test on natural durability of the Siberian larch heartwood timber. The test has been conducted in Finland according to the European norm EN252 since the year 2006. The material is timber imported from natural larch stands in Ust-Ilimsk, Russia, and cultivated larch stand in Punkaharju, Finland. The Finnish stand is growing outside the natural range of distribution of Siberian larch. Untreated Scots pine heartwood and impregnated Scots pine sapwood were used as reference materials. The results after 11 years showed that there was remarkable variation in the durability between the larch heartwood samples. Nevertheless, the most durable timber lots on average were the Siberian larch heartwoods harvested from the Russian native stands and the Finnish cultivated stand. It is predicted that it will take another 10 years or more until the failure of the most durable larch stakes.