A field study was conducted on floral biology and artificial pollination in soursop (Annona muricata L.). Although flowers are apparently adapted to cross pollination despite being anatomically hermaphrodite, the bunched arrangement of stamens does not results in available fertil pollen. There is a period from 36 to 48 hours in which both sexual organs are simultaneusly, however guanabana flowers functions as physiologically protogineous. None insect genera has any influency on poIlination. It is assumed that generally fruits are formed by autogamy after stigmas get in contact with stamens retained by lower petals. Because this way of pollination is rather sporadic and sometimes stigmas shed after pollination but before fertilization, only a low number of fruit setting is observed as many flowers fall out due to the low number that get fertilized. Manual poIlination resulted in an effective way to increase production. The size and growth rate of these fruits are correlated with the number of pistiIs get fertilized.