For the purpose of graphical analysis and estimation of genetic parameters related to yield and its
components, six tobacco genotypes was crossed in half -diallel mating design. In this study, the F2
progenies and their parents were evaluated in a randomized complete block design with three
replications. The results of analysis of variance indicated a significant difference between genotypes
for plant height, leaf number, leaf dry weight and leaf fresh weight. Hayman graphical method was
utilized for analysis of data. Diallel analysis indicated existence of an additive and dominant actions in inheritance of all studied traits. Traits including plant height, leaf number, leaf length and width, stem diameter, internode distance and leaf dry weight possessed greater additive effects meanwhile in the leaf weight the dominance effect was greater. The additive gene action detected for leaf dry weight (yield) manifested the influence of selection methods in breeding of this trait. Due to the fact that the fresh weight of the leaf was controlled by dominance effects, so hybrid-based methods are effective in modifying this trait. Also, additive and dominance gene action were contributed in heritability of yield, plant height and number of leaves. Regarding the mean values of dominance degree and results of graphical analysis, the gene action for leaf fresh weight was over-domnance and so, the heterosis phenomenon could be used to increase and improve this trait. For the traits including plant height, leaf number and yield, the gene action type was relative dominance.