Over the last 10 years, several species of the genus Phaeoacremonium have been reported from various woody trees worldwide. Species of this genus as vascular plant pathogens can infect a wide range of ornamental, forest and fruit trees. Between 2013 and 2016 several surveys were conducted throughout Guilan province with the aim of isolating and identifying fungal trunk pathogens associated with forest trees. Branches showing yellowing, cankers and dieback were collected from trees at various forest regions. Fungal isolations were made from the edges of necrotic wood lesions of samples displaying disease symptoms. From each sample, 15 to 20 small segments were cut and surface disinfected by immersing in 0.5% solution of NaOCl for two min and rinsed in sterile distilled water (SDW). Wood segments placed into Petri dishes containing potato dextrose agar (PDA) or malt extract agar (MEA) supplemented with 100 mg L-1 of streptomycin sulphate. Plates were incubated at 25°C in the dark until mycelial growth could be detected from wood pieces. In this study nine isolates of Phaeoacremonium spp. were obtained from Alnus glutinosa (five isolates) and Quercus castaneifolia (four isolates). Morphological characters used to distinguish these isolates included colony characters and pigment production on MEA, PDA and oatmeal agar (OA) and microscopic observations (phialide type and shape, conidiophore morphology, size of hyphal warts and conidial size and shape). For these isolates, ± 300 bp. of the 5′ end of the actin (using ACT-512F and ACT-783R primers) and ± 600 bp. of the 5′ end of the beta tubulin (using T1 and Bt2b primers) genes were amplified. Based on the DNA sequence analyses and morphological characters, all isolates obtained from A. glutinosa trees were identified as Phaeoacremonium subulatum, while isolates recovered from Q. castaneifolia were identified as Phaeoacremonium inflatipes. Sequences of two isolates derived in this study, IRNHM-KZ16 (P. sabulatum, GenBank Accession No. ACT: MG456745 and BT: MG456737) and IRNHM-NPEPS2 (P. inflatipes, GenBank Accession No. Act: MG456744 and BT: MG456743) were lodged at GenBank. This is the first report of P. subulatum on A. glutinosa and P. inflatipes on Q. castaneifolia in the world. This study also represents the first record of P. subulatum from Iran.