The detailed structure of counter-flow, ethylene diffusion flame has been studied under atmospheric conditions. The temperature and mole fraction profiles of major, minor, aromatic and polycyclic aromatic hydrocarbon (PAH) species have been determined under the strain rate of 56.6 s(-1). Flame sampling was achieved by using a heated quartz microprobe connected to a silica-coated stainless steel sampling line which transferred the sample to an on-line Gas Chromatograph/Mass Spectrometer (GC/MS). Rapid insertion method was used to obtain the temperature profiles with a silica coated Pt/Pt + 13% Rh thermocouple. Visually, the name showed 3 different color zones: Blue, yellow and orange. The blue zone with a maximum flame temperature of 1577 degreesC was located in the oxidizer side of the flame. The most abundant hydrocarbon pyrolysis product was C2H2, which was located in the yellow zone. Benzene was measured as the most abundant aromatic species with 220 ppm maximum level, located in the yellow zone. Naphthalene (50 ppm) and pyrene (5 ppm) were the most abundant PAH formed. Increasing strain rate resulted in decreasing residence times and cooler flame temperature thereby leading to the observation of fewer number and lower peak levels of aromatics and PAH when compared to the lower strain rate ethylene flame studied before (Olten and Senkan, 1999).