ABSTRACT Twenty-six genotypes of sunflower (16 F1-hybrids, four female lines, four restorer lines and two check varieties; Sakha 53 and Giza 102) were evaluated under two contrasting environments, i.e., loamy sand soil at A.R.C., Arab El-Awamer Res. Stn., and clay soil at Assiut Univ. Exper. Farm in season 2016. Genotypes mean squares of the studied traits was significant (P0.01) either in the separate or in the combined analysis. The differences between the two environments were significant for all traits except head diameter (HD). The genotype x environment interaction was significant for all traits, indicating differential responses of genotypes to the two environments. The sixteen hybrids showed negative significant heterosis (P0.01) for 50% flowering from the earlier check Giza 102 (standard heterosis; SH %), which ranged from -8.39 to -18.44% under loamy sand soil, and from -2.80 to -12.92% under clay soil. The heterotic effects were higher under loamy sand than under clay soil. The combined data showed that 4, 5 and 12 hybrids were significantly earlier than the mid-parent, better parent and the earlier check; respectively. The combined data over the two environments of plant height indicated that 15 hybrids showed negative significant standard heterosis ranged from -8.42 to -25.16%. This gives a good opportunity to select short sunflower hybrids. All the hybrids showed negative SH% for head diameter, and none of them exceeded the check variety in 100-SW. Otherwise, all the hybrids showed negative significant (P0.01) heterosis in husk% from the better check Sakha 53 either at the two environments or at the combined data. Over environments the SH% in oil% was positive and significant (p≤ 0.01) for four hybrids (ranged from 4.47 to 9.83%), for three hybrids in kernel weight and for one hybrid in number of seeds/head. Mid-parent heterosis in seed yield/head was positive and significant (P0.01) for 14 and 13 hybrids under loamy sand and clay soil; respectively, eight and three hybrids showed positive and significant BPH heterosis in seed yield/head under the respective environments. The positive and significant (P0.01) BPH in seed yield/head ranged from 16.54 to 685.33% under loamy sand soil, and from 13.42 to 70.38% under clay soil. Otherwise, only one hybrid No. 1 (A7 x Rf1) gave positive significant (P0.01) heterosis from the check hybrids Sakha 53 under clay soil and combined data. Mid-parent heterosis in oil yield/head was positive and significant (P0.01) for 14 hybrids under both environments and ranged from 3.35 to 823.12% under loamy sand, and from 3.01 to 151.88% under clay soil. Eight and three hybrids gave positive significant (P0.01) BPH under loamy sand and clay soil; respectively. The BPH in oil yield/head ranged from 9.48 to 708.95% and from 3.91 to 66.06% under the two respective environments. Standard heterosis in oil yield/head from the better check cultivar was positive and significant for five hybrids under loamy sand, one hybrid under clay soil and two hybrids in the combined data. Key words: Heterosis, Helianthus annuus L., Standard heterosis