The rapid progress of microfluidics has contributed to modern analytical methodology. However, in situ integration of chemical/biological sensors for on‐chip reaction monitoring remains a big challenge. Herein, reported is the fabrication of an integrated surface‐enhanced Raman scattering (SERS) sensor and graphene‐based catalytic chip by laser scribing of graphene oxide (GO) and Ag nanoparticles (AgNPs) composite (AgNPs@GO). The surface plasmonic effect of AgNPs can promote the photoreduction of GO, inducing a high porous nanostructure. By combining the AgNPs@RGO nanocomposite patterns with polydimethylsiloxane microfluidic channels, a bi‐functional microfluidic chip capable of on‐chip catalysis and SERS detection is fabricated. As a proof‐of‐concept demonstration, on‐chip AgNPs‐catalyzed 4‐nitrophenol (4‐NP) reduction has been implemented, in which the reaction process can be well monitored using the in situ SERS sensor. The integration of SERS sensors with functional microfluidic devices may hold great promise for developing advanced Lab‐on‐a‐Chip systems.