Eighty five lichens are reported for the first time from Doui-Thabet forest, Saïda province, Algeria, four of them (Acarospora aeginaica, Acarospora calcivora, Acarospora pitardii, Acarospora xanthophana) are new to Algeria. Of them Acarospora aeginaica is reported for the first time to north Africa. Ten of the recorded species are protected under the Algerian endangered species legislation. For all newly recorded species descriptions of morphology, anatomy, ecology and distribution are provided. Keywords: lichenized fungi, diversity, Doui-Thabet forest, northern Africa.