Thaumetopoea ispartaensis Doganlar and Avc1 (Lepidoptera: Notodontidae) (cedar processionary moth: CPM) is one of the most dangerous pests of Cedrus libani A. Rick living in abundance in forests of the Isparta region and some forests of Taurus Mountain in Southern Turkey. The present study was conducted to study the biology of T. ispartaensis which was recorded and defined first time in Turkey and its damage on cedar needles. The study was conducted in Isparta-Senirkent Kapidag Forests (between 1250 and 1650 m; 38 degrees 06' N, 30 degrees 45' E) where the pest caused most damage. It was determined that T. ispartaensis was a monophagous species of C. libani. The flight period of the pest lasted from mid-August to mid-September. Females laid eggs underside of twigs (mean 3.5 mm diameter) on the lower part of trees. Eggs were covered by scales which were colored similar to the bark of shoot. Egg numbers of egg batches varied between 39 and 245 (mean 121). The caterpillars started to hatch in the second half of April, and it had five instars. The caterpillar hatching rate from eggs was found as 87.5%. The caterpillars which built the nests on stems and shoots fed at nights and stayed in their nests in the daytime. Mature larvae started to pass into the soil for pupating from the beginning of July. The pupation was determined in the first half of July, in a depth of 5-15 cm of soil, in the sun-exposed places in cedar woods along the sides of the roads. T. ispartaensis was determined as univoltine species.