G-quadruplexes are four-stranded nucleic acid structures that play vital roles in regulating gene expression, maintaining genomic stability, and supporting various biological processes. This protocol details their formation from double-stranded DNA via in vitro transcription. It includes steps for selecting suitable DNA templates, assembling necessary components (such as RNA polymerase, nucleotides, and buffers), setting optimal incubation conditions, and performing dimethyl sulfate (DMS) footprinting to analyze the structures. For complete details on the use and execution of this protocol, please refer to Zhang et al.