Abstract: Observations were carried out on morphological and biological properties of flowers and fruits of introduced 5-year Citrus grandis in Chengmai of Hainan province. The results showed that the complete flower consists of receptacle, calyx, flower stalk, petal, pistil, stamen, and honey disk, with petals of 4-6, length of 30-35 mm, stamen of 28-35, yellow anthers, white filaments, length of 19-22 mm, honey disc diameter of 6-8 mm. The pollen is nearly round, with four germinal furrows, the pollen grain has size of 18.37μm×25.13 μm (polar axis length×equatorial axis length), and the extine looks like net, with different holes. The fruits growth curve is single S, with the whole growth period of 170 days. Average soluble solid content of fruit is 13.3%, average content of titratable acid is 0.46%, the average content of vitamin C is 40.5 mg/100 g, and the average water content of sarcocarp is 85%. The observation results on the biological characteristics of Citrus grandis flowers and fruits can provide theoretical basis for the efficient and high-quality cultivation and production management technology in hainan