To evaluate the gene effect, heritability and correlations of ajowan (Carum capticum L.) morphological traits ten parents were chosen from a genetically broad-based population and polycrossed to produce half-sib families. The evaluated traits were number of days to flowering, plant height, number of fertile branches, number of umbrellas per plant, number of seed per umbel, seed yield per plant, harvest index, essential oil percentage, essential oil yield. Parents and polycross progenies seeds were grown in a randomized complete block design with three replications in the University of Tehran research field, during 2015-2017. The results showed that in parents and their progenies broad-sense heritability ranged from 0.64 to 0.96. Narrow-sense heritability based on regression of progenies on the parents (h2po) and analyses of progenies (h2n) suggested that additive genes control these traits. Correlation of seed yield with plant height, number of fertile branches, number of umbrellas per plant and number of seed per umbel were positive and significant. The results indicated that there were significant negative correlation between thymol and γ- terpinene both in parents and half-sib families. We concluded that there were significant variation and high heritability for most of the evaluated traits in the ajowan populations to improve seed yield and essential oil yield.