Engineering functional vascular networks in vitro is critical for tissue engineering and a variety of applications. There is still a general lack of straightforward approaches for recapitulating specific structures and functions of vasculature. This report describes a microfluidic method that utilizes fibrillogenesis of collagen and a liquid mold to engineer three-dimensional vascular networks in hydrogel. The well-controlled vascular network demonstrates both mechanical stability for perfusing solutions and biocompatibility for cell adhesion and coverage. This technique enables the mimicry of passive diffusion in a nephron one of the main routes transferring soluble organic molecules. This approach could be used for in vitro modelling of mass transfer-involved physiology in vasculature-rich tissues and organs for regeneration and drug screening.