Many applications in micro-tissue engineering need to use concave microwells and microchannels to mimic the in vivo microenvironment, such as the culture of spheroids and construction of artificial blood vessels. Here, we propose a novel method of fabrication of concave microwells and microchannels by off-stoichiometry thiol-ene (OSTE) backside lithography. At first, we use OSTE backside lithography to fabricate convex microstructures on a solid substrate assisted by a diffusing glass. Then we use the solid substrate for replica molding of gelatin or agarose gel to get concave microwells and microchannels on a gel substrate. Our method brings convenience for the fabrication of concave microwells and microchannels, and can find potential applications in micro-tissue engineering immediately.