Abstract: There is a few researches about the development of pituitary of teleost fishes.In China,there is only reports about that of Ctenopharyngodon idellus and Hippocampus japonicus.Silurus meridionalis or Silurus soldatovi meridionalis, is a kind of Siluridae fish of quick growth,strong anti-infection and high value.Some scientists has made research about the development of its embryonic and larva,but there is still no report about the development of its pituitary. The article investigated the different development periods in the aspects of histology,histochemistry and ultrastructure.The fish of embryonic and prolarval stage and postlarval stage were from artificial fertilization,hatch and feed at constant temperature(21±0.5℃).They were fixed in Smith liquid,Bouin liquid,carnoy liquid,dyed by H.E,PAS-OG(periodic acid Schiff’s orange G),Heidenhain Azan respectively.The juvenides of six-months old,1 year old and 2 years old were collected from the cages in Jialing river,fixed in Bouin liquit,formaldehyde-hydrargyrum,respectively,dyed by PAS-OG,PAS(periodic acid Schiff’s),AF(Aldehyde fuchin),PFA-AB(periodic acid Alcian blue,dye their nucleus in azocarmine),Azan,respectively.The steps of ultrastructure research was as follows:firstly,according to the location of pre-adenohypophysis,meta-adenohypophysis,mesoadenohypophysis and neurohypophysis under the microscope,the pituitary of larvas were divided into four parts,and they were fixed in glutaraldehyde of 4 percent(4℃)for 24 hours,respectively,then,they were fixed in osmic anhydride of 1 percent(4℃)for 3 hours,Secondly,they were dehydrated in series of acetone,and embeded in Epon812 Thirdly,they were made hemithin sections,dyed in aniline blue of 1 percent,observed and located under the microscope.Finally,they were made ultrathin sections,dyed in uranium acetic and lead citrate,observed and taken photos with H-300 transmission electron microscope. The results indicate that the pituitary of Silurus meridionalis origins from the epithliu cells of the original cavum oris during embryo and from the cells which were separated from the infundibulum.The former composes pre-adenohypophysis,mesoadenohypophysis and part meta-adenohypophysis and the latter forms neurohypophysis and part meta-adenohypophysis.32h after fertilization,the epithelia cells of the original oral cavity proliferate,the cells in wall of oral top sunken-in and begin to emigrant inwards.38h after fertilization,the epithelia cells depart from wall of oral top and form solid cellular lump,then emigrant towards infundibulum.45h after fertilization,solid cellular lump emigrant to the infundibulum.The epithelium cells of the original cavum oris locates at the bottom of the diencphalon in just hatched juvenile and touches the infundibulum,and zygosised with those cells originated from the infundibulum by 36h after hatching;by 48h the pituitary can be distinguished into two parts:adenohypophysis and neurohypophysis;by 4d the adenohypophysis is divided into two portions;by 6d the growth hormone cells differentiate;by 10d pre-adenohypophysis,mesoadenohypophysis and meta-adenohypophysis form;by 48d the morphological endocrine cell types except for gonadotrophs in adenohypophysis had differentiated;by 6 months all types of morphological endocrine cell in adenohypophysis finished differentiation.The morphology and histological structure of the pituitary are similar to the adult’s.The difference in the pituitary of fish between the six-months larva and the one or two year old juveniles is only in the volume of pre-adenohypophysis,mesoadenohypophysis,meta-adenohypophysis,the rate of gland cells and the ultrastructure of some secreting cells.