Morphological development of feeding organ of Oreochromis niloticusvarying from 6. 0 mm to 223. 0 mm in total length (n271) was observed throughdissection, sectioning, light and scanning electron microscopy. The followingsubjects were described:1. Development characteristics of gill rakers, buccal palatine, jaw teeth, andpharyngeal teeth;2. Changes in quantitative traits of feeding organ with development, i. e.mouth size (opening),number, density,and length of gill raker, distance betweenthe adjacent gill rakers, number, density and length of lateral protuberances onfiltering lamellae,and distance between lateral protuberances.The following quegtions were also discussed:1. Relationship between feeding mode and feeding function in Tilapia;2. Relationship between development of feeding organ and transition of feeding mode;3. Relationship between changes in quantitative characters of feeding organsand transition of the size-suitability and composition of food:4. Relationship between development of feeding organs and biological technique for Tilapia culture.