Abstract: In order to find out the rules of the meso-nephric genesis and nephron. s development of the fishes, the embryos, larvae and juveniles of Silurus meridionalis for experimentat ion, which were hatched by controlling the temperature, were fixed in Smith. s, Boun. s, and Carnoy. s liquid from March, 2001 to March, 2002. The methods of histology and histo-chemistry were applied to study the development of the kidney in the catfish. The results are indicated as following: The genesis of mesonephros started at 24h after hatching. The process of mesonephric genesis and nephron development includes the mesenchymal cells assembling stage from 24h to 48h after hatching which divided and assembled into mesonephrogenic bridge, the mesonephric vesicle and the renal tubule bud forming stage from 4d to 5d after hatching, the development stage of primary nephron from 6d to 10d a-fter hatching, the primary nephron maturing and the sublevel, the third class nephron forming stage from 16d to 19d after hatching. When the pronephron was disintegration at 19d after hatching, the primary nephron started to work. In the kidney of larvae or juveniles between three months and two years, there are a lot of mesenchymal cells and developing nephrons in various stages:the prodefferentiation stage, the different iation stage, the developing stage and the mature stage. The prodifferentiation stage is the forming of mesonephrogenic cellular mass and renal tubule bud. The renal tubule different iates into proximal segment in the differentiation stage. The renal tubule differentiates into every discriminating segments in the developing stage. The nephron is working in the mature stage. It is obvious variations with adult. s renal tissue. Especially there are abundant in large PAS-positive granule in epithelia of the primary proximal segment because the nephron is premature and the glomerulus is easily permeable. There are a large number of developing nephrons in kidney of the larvae or juveniles between three months and two years.