We describe a facile and low-cost approach for flexible integration surface-enhanced Raman scattering (SERS) substrate in microfluidic chips. Briefly, a SERS substrate was fabricated by electrostatic assembly of gold nanoparticles, and shaped into designed patterns by the subsequent lift-up soft lithography. The SERS micropattern could be further integrated within microfluidic channels conveniently. The resulting microfluidic SERS chip allows one to ultrasensitively in-situ SERS monitor from the transparent glass window. With its advantages in simplicity, functionality, and cost-effectivity, this method can be readily expanded in optical microfluidic fabrication for biochemical applications.