Vegetables have a critical function in human health and nutritional security. Vegetables are considered an essential building block of any diet. Out of the leafy vegetables, Amaranthus is the most popular and salable vegetable consumed by people all over India. Seed processing experiment was undertaken in Amaranthus tricolor (CO 2) by using the sieves placed inside the mechanical seed shaker (Gyratory sieve shaker) to improve the quality of Amaranthus seeds. The seeds of Amaranthus were size graded with seed shaker attached with various sieve size of BSS 18 X18 (R), BSS 20 X 20 (R), BSS 22 X 22 (R) and BSP 22 X 22 (P). During processing, the machine could be adjusted for 2, 3, 4 and 5 minutes with an oscillating speed of 1440 rpm. The separated seeds were evaluated for seed quality characteristics such as seed germination percentage, shoot length, root length, dry matter production, 1000 seed weight and seed recovery percentage. The results revealed that the sieve size of BSS 22 X 22 (R=retained) mesh sieve had the better quality seeds with a maximum recovery of 67.41 g and when it is operated for a period of 5 minutes. The germination percentage was improved from 77 % to 95 % with 1000 seed weight of 73.21 mg, and the observed recovery was 56 per cent with the vigour index of 1145. Hence, BSS 22 X 22 retained mesh sieve with a duration of 5 minutes could be recommended as an optimum sieve size for grading Amaranthus seeds for improving the seed quality. [ABSTRACT FROM AUTHOR]