Tetraploids are desired to produce seedless fruits. In order to produce an autotetraploid population in watermelon (Citrullus lanatus Thunb) by colchicine. four treatment methods were examined ( dry seeds, soaking of germinated seeds and the meristem tip of the seedlings at the emergence of two true type leaves beside the control treatment ) to determine the best treatment for the induction of tetraploid plants. Autotetraploid plants were produced by all treatments with colchicines. meristem tip treatment at two true leaves stage proved to be the most effective in obtaining autotetraploids. In order to distinguish the induced colchicines tetraploid plants from the diploids, morphological change and techniques as number of chloroplast per guard cell and pollen grain diameter were considered and proved that these methods are suitable, quick and easy for identification to the ploidy level of watermelon cv. Sugar Baby. The chromosome scoring in watermelon plants was 22in plants diploid (2n = 2x = 22) and44 in tetraploids (2n = 4x = 44). Tetraploid produced plants with short stem length but dark green leaves with great amount of branches per plant and chlorophyll content compared to diploid plants. Less amount of fruits per plant, fruit weight, TSS and number of seeds per fruit were noticed in tetraploid plants as compared with diploid plants. The seeds of diploid were oblong whereas the tetraploids varied from oblong to round.