AIM:To investigate the changes of microvasculararchitecture,ultrastructure and permeability of rat jejunalvilli at different ages.METHODS:Microvascular corrosion casting,scanningelectron microscopy,transmission electron microscopy andEvans blue infiltration technique were used in this study.RESULTS:The intestinal villous plexus of adult rats consistedof arterioles,capillary network and venules,The marginalcapillary extended to the base part of the villi and connectedto the capillary networks of adjacent villi.In newborn rats,the villous plexus was rather simple,and capillary networkwas not formed.The villous plexus became cone-shapedand was closely arrayed in ablactation rats.In adult rats,the villous plexus became tongue-shaped and was enlargedboth in height and width.In aged rats,the villous plexusshrank in volume and became shorter and narrower.Thediametral ratio of villous arteriole to villous venule increasedas animals became older.The number of endothelial holes,the thickness of basal membrane and the permeability ofmicrovasculature were increased over the entire course ofdevelopment from newborn period to aged period.CONCLUSION:The digestive and absorptive functions ofthe rat jejunum at different ages are highly dependent uponthe state of villous microvascular architecture andpermeability,and blood circulation is enhanced by collateralbranches such as marginal capillary,through which blood isdrained to the capillary networks of adjacent villi. AIM: To investigate the changes of microvasculararchitecture, ultrastructure and permeability of rat jejunalvilli at different ages.METHODS: Microvascular corrosion casting, scanningelectron microscopy, transmission electron microscopy and Evans blue infiltration technique were used in this study .RESULTS: The intestinal villous plexus of adult rats consisted of arterioles, capillary network and venules, the marginal capillary extended to the base part of the villi and connected to the capillary networks of adjacent villi. newborn rats, the villous plexus was rather simple, and capillary networkwas not formed. The villous plexus became cone- shapedand was closely arrayed in ablactation rats.In adult rats, the villous plexus became tongue-shaped and was enlargedboth in height and width.In aged rats, the villous plexusshrank in volume and became shorter and narrower.Thediametral ratio of villous arteriole to villous venule increasedas animals became older. number of endothelial holes, the thickness of basal membrane and the permeability of microrovasculature were increased over the entire course of development from newborn period to aged period. CONCLUSION: The digestive and absorptive functions of the rat jejunum at different ages are highly dependent uponthe state of villous microvascular architecture andpermeability, and blood circulation is enhanced by collateralbranches such as marginal capillary, through which blood isdrained to the capillary networks of adjacent villi.