As a summer crop, sunflower is influenced a lot by environmental conditions, so sunflower yield changes frequently year by year. On the other hand, in the recent years’ temperatures increased daily or periodically due to global warming. Therefore, new breeding studies should focus mostly to develop sunflower hybrids having high drought tolerance. Based on these priorities, the study was conducted to evaluate the effects of drought stress on plant height, head diameter, flowering and physiological maturity period of some male inbred lines developed previously by Trakya Agriculture Research Institute (TARI). In this study, there were big changes among male lines on tolerance levels of yield traits under controlled conditions to drought. The significant effect of drought stress was determined on head diameter among examined yield traits. However, plant height affected less from drought stress. While head diameter of plants reduced up to 50%, drought stress conditions decreased the days of flowering up to 20% (about one week) of flowering time and about 15% (about 11-12 days) of physiological maturity period. Sunflower lines were screened for improved drought tolerance based on drought factor index (DFI) calculated for head diameter values.