P>The North Anatolian Fault Zone (NAFZ) is a transform structure that constitutes the boundary between the Anatolian Plate to the south and the Eurasia Plate to the north. We analysed the properties of the upper-mantle strain field and mantle anisotropy in the vicinity of NAFZ via splitting of SKS and SKKS phases. We used data from the North Anatolian Fault (NAF) passive seismic experiment. This is the first study that analyses the upper-mantle anisotropy in this region and our results indicate that the observed upper-mantle strain field is uniform underneath the array with consistent NE-SW polarization directions for fast split waves. The measured lag times between the arrivals of the fast and slow split waves varies from 0.5 to 1.6 s for the study area. Smaller lag times are obtained consistently in the eastern part of the array. However, we do not observe any significant variation in either the polarization directions or the delay times across the plate boundary (NAFZ).