The precise and predictable formation of double-helical structures from complementary DNA sequences has made DNA an extremely versatile tool for programming self-assembled structures from the nanometer to micrometer scale. While a number of supramolecular interactions have been shown to drive self-assembly of macroscopic building blocks of the millimeter scale, DNA-driven self-assembly of macroscopic objects has not been well-established. In this work, we developed a postpolymerization coupling strategy to conjugate short DNA sequences to polyacrylamide-based hydrogel blocks. We observed sequence-specific self-assembly of DNA-decorated hydrogels with 1-2 mm edges in aqueous solution. Furthermore, selective disassembly of hydrogels upon addition of a DNA strand was demonstrated by exploiting a strand displacement reaction. These results lay the foundation for adaptation of various DNA functions to macroscopic self-assembly, for example, molecular recognition, molecular computation, and chemical catalysis.