In the olive orchard on the western part of Istria, Croatia, twig and branch dieback was observed on several olive trees from the local cultivar ‘Buza’. In total, seven samples from symptomatic trees were collected. Samples were analyzed, and four fungal isolates showed morphological similarities to the species Phaeoacremonium iranianum. One isolate, chosen as a representative, was taken for molecular identification and pathogenicity tests. Based on DNA sequence data of ITS1/ITS4, βt2a/βt2b, EF1-728F/EF1-986R, the isolate was identified as P. iranianum. Pathogenicity tests were conducted on detached olive branches and olive trees in the greenhouse, and identified fungal species was pathogenic on olive. To the best of our knowledge, this is the first report of twig and branch dieback on olive causing by phytopathogenic specie of fungus Phaeoacremonium iranianum.