Tai Nguyen variety is a local seasonal rice variety, grown in some districts in Tra Vinh province. This rice variety has delicious rice and is highly adaptable to acidic and saline soils in the Mekong delta. Phenotypic variation of agronomic characters was investigated to eliminate the genetic diversity of the Tai Nguyen populations. Forty G1 individuals with the same maturing day and uniform agro-morphological characteristics were selected for G2 generation at 3 locations as Chau Thanh, Tra Cu and Cau Ngang of Tra Vinh province. The agronomic indexes of 40 Tai Nguyen rice lines in the G1 crop reached the following average values such as culm length 128.8 cm, number of branches 40.5, leaf length 53.4 cm, leaf width 1.0 cm, number of panicles 34.8, panicle length 24.7 cm, total number of firm seeds 134.3, total number of seeds 170.7, grain length 8.4 mm, grain width 2.4 mm, dry weight 193.0 g, and weight of 1000 grain 22.9 g. The comparison results have selected the 13 best G1 lines to be used as raw materials for the G2 crop