Wheat is the most important food crop in Iran. our country. Biotic stresses including plant diseases are considered as main limiting factors in wheat production. Stem rust (black rust) caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most important wheat diseases, worldwide. Stem rust had been controlled by exploiting effective Sr resistance genes in genetic structure of the host plants as resistant cultivars in international wheat breeding programs. The wheat resistance gene Sr31 had been built a durable resistance to the disease for more than 40 years. In 1999, first virulence on Sr31 was observed due to a new Pgt race in Uganda, called race Ug99, and was identified as race TTKSK. Emergence and spreading Ug99 and its variants highly threatened wheat global production by nullifying Sr31, and breaking the host resistance. Subsequently, this race was reported from Kenya, Ethiopia and Yemen in 2002, 2003 and 2006, respectively. In Iran, TTKSK was first reported from Boroojerd and Hamedan in 2007, and then from Ahwaz and Dasht-e Azadegan in 2009. The race was spread to Kelardash and Shawoor in 2013 and 2016, respectively. In order to track race TTKSK in Northwest of Iran, infected stem and leaf samples were collected from wheat fields of East and West Azarbayjan provinces in 2016. Samples were then transferred to stem rust green house (Department of Cereal Research, Seed and Plant Improvement Institute, Karaj, Iran). Purification and multiplication of Pgt isolates were done on susceptible wheat cultivar McNair 701. North American (NA) differential set (consisting 20 wheat cultivars) was used for determining effectiveness of resistance genes as well as race identification of the isolated. In total, 30 seedlings (in 3 replicates) per each cultivar were inoculated by purified urediniospore suspension of isolates in Soltrol 170 oil. Infection types were evaluated as reaction of the genotypes based on 0-4 Stakman et al. (1962) scale at 14 days post inoculation (dpi), and Pgt races were identified based on Roelfs et al. (1992) coding system. Based on the results, an isolate collected from Hashtrood region of East Azarbayjan province showing virulence to Sr31 resistance gene, was identified as race TTKSK. This finding as the first report of TTKSK from East Azarbayjan, shows spreading of Ug99 race towards Northwest of the country. Our results prove the necessity of replacing nullified Sr genes with effective genes conferring resistance to Pgt isolates in wheat breeding programs, particularly for Iranian Cold climatic zone.