This study was undertaken to assess heterosis and heterosis parameters of viscosity characters in rice with the aim of evaluating the using of hybrid base methods for improving rice cooking quality. F 2 progenies, from a 6×6 half diallel with their parents planted in a complete randomized block design with three replications at Rice Research Institute of Iran in 2015. The analysis of variance of RVA parameters through Gardner-Eberhart II method showed that mean square of genotype was

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... for all viscosity characters. Also, mean square of variety and heterosis were significant for all studied traits. Average heterosis was significant for PV, FV and SV. Variety heterosis and specific heterosis were significant for traits PV, BV, FV and SV. Estimation of the variety effect (v i ) and heterosis of varieties (h i ) for viscosity characters revealed that the parent Line 23 had the most contribution to heterosis for PV, BV and FV. Use of this parent in hybrid base breeding methods will be promising to improving these traits. The highest estimate of v i observed in the parent RI18430-46 for PV and FV, parent Deylamani for BV and parent IR50 for SV. Therefore, use of these parents in selection base methods to improving these traits is promising. Results of relative heterosis through mid-parents and heterobeltiosis for viscosity characters in rice crosses revealed that heterobeltiosis for peak viscosity, breakdown viscosity, final viscosity and setback viscosity had a range of -14.39% to 13.10%, -57.01% to 59.86%, -13.41% to 8.85% and -22.45% to 29.10%, respectively.