A population of a new species of Deladenus was recovered from the natural Golestan Forest Park in Golestan Province, northern Iran. This species is characterized by a body length of 450–733 µm, a short stylet measuring 6.0–7.5 µm, seven to eight lateral field incisures, a fusiform median bulb lacking a median chamber, an excretory pore located at the level of the hemizonid and near the terminus of the basal esophageal bulb, and the absence of a posterior uterine sac. The new species closely resembles D. gilanica and D. hyrcanus but can be distinguished from D. gilanica by its longer body length (450–773 vs. 314–422 µm), shorter stylet (6.0–7.5 vs. 7.5–8.0 µm), longer tail (34–58 vs. 27–32 µm), greater vulva–anus distance (20–37 vs. 15–26 µm), and more posteriorly positioned excretory pore (opposite the end of the dorsal esophageal gland). It differs from D. hyrcanus in body length (450–773 vs. 718–806 µm), stylet length (6.0–7.5 vs. 7.5–10.0 µm), excretory pore position (near the end of the basal bulb vs. anterior to the basal bulb), and tail length (34–58 vs. 58–72 µm). Additionally, sequences of the small and large subunit ribosomal DNA regions (SSU and LSU D2–D3) were obtained, and phylogenetic analyses were conducted. The proposed new species, Deladnus golestanicus, is supported by the morphological and morphometric distinctiveness of the resulting phylogenetic trees.