A process for preparing butadiene, comprising A) providing a stream (a) comprising n-butane; B) feeding stream (a) comprising into at least one first dehydrogenation zone and nonoxidatively catalytically dehydrogenating n-butane to obtain a stream (b) comprising n-butane, 1-butene, 2-butene, butadiene, hydrogen and low-boiling secondary constituents; C) feeding stream (b) and an oxygenous gas into at least one second dehydrogenation zone and oxidatively dehydrogenating n-butane, 1-butene and 2-butene to obtain a stream (c) comprising n-butane, 2-butene, butadiene, low-boiling secondary constituents, carbon oxides and steam, wherein stream (c) has a higher content of butadiene than stream (b); D) removing the low-boiling secondary constituents and steam to obtain a stream (d) substantially consisting of n-butane, 2-butene and butadiene; E) separating stream (d) into a stream (e1) consisting substantially of n-butane and 2-butene and a stream (e2) consisting substantially of butadiene by extractive distillation; F) recycling stream (e1) into the first dehydrogenation zone.