Highly active, stable and affordable surface enhanced Raman scattering (SERS) substrates were obtained by electrolyzing a mixture of AgNO3 (4 ×10-4 mol/L) and Na3C6H5O7H2O (6 ×10-5 mol/L) for 1, 2, 3 and 4 h at 7 V. With crystal violet (CV) as a test molecule, a portable Raman spectrometer with 785 nm laser excitation was employed to carry out the SERS detection. Colloidal Ag nanoparticles prepared by electrolyzing for 3 h with the particle size of (65 ± 17) nm is a perfect SERS substrate for the ultratrace detection of CV, which displayed an enhancement factor of ca. 1.3×108 and the detection limit of CV is down to ca.10-15 m01/L (ca. 10-4 ppb) with 10-1 mol/L KBr as aggregating agent. Thus, this SERS substrate will provide a hopeful foreground in ultratrace detection. Meanwhile, it will provide a possibility to bring Raman analysis out of the laboratory to process in situ, real-time detection and identification.