Eldar pine (Pinus eldarica Medw., Pinaceae) is among the most popular and commonly planted ornamental trees in Northern and Central Iran. Rust infected specimens of Eldar pine were collected from pine cultivated forest at Hezaar-Pich, Gorgan, Golestan province, in April 2012 and submitted to the Botany Department of Iranian Research Institute of Plant Protection, Tehran for diagnosis. The specimens showed heavy rust diseases symptoms including aecia on needles of Eldar pine. A description of the causal agent follows: Spermogonia subepidermal, on both sides of infected leaves. Aecia mostly hypophyllous, develop as conspicuous white columnar pustules on pine needles, peridermioid, with strongly developed bullate or tongue-shaped peridium, 1.5-3 x 0.5 mm and up to 1.2 mm high. Aeciospores catenulate, 25-40 x 17.5-26.5 µm, ellipsoid, oblong ellipsoid or more or less globoid, spore wall covered by rod-like verrucae (verrucose), wall including verrucae 2.5-4 µm thick, discrete rods up to 2.5 µm high, occasionally reduced on one side of spores or united in irregular or pseudoreticulate patterns (Fig. 1). Based on infection pattern and above mentioned morphological features of aecia and aeciospores, the rust fungus was identified as Coleosporium tussilaginis (Pers.) Lev. (Majewski 1977). The voucher specimen, 17001F, was deposited in IRAN, Iranian Research Institute of Plant Protection, Tehran. This is the first report of C. tussilaginis on a member of Pinaceae in Iran. Moreover, Pinus eldarica, is reported as a new host for the rust. Coleosporium tussilaginis is a heteromacrocyclic rust with telial stage on members of Asteraceae family including species of the genera Tussilago, Senecio, Petasites and Sonchus (Braun 1981).