Objective：To construct highly sensitive surface-enhanced Raman scattering (SERS) sensor and implement the rapid detection of trace formaldehyde from human urine. Methods：A novel SERS sensor was fabricated by modifying p-aminothiophenol (p-ATP) on the surface of Ag nanoparticles (Ag NPs). When the aqueous formaldehyde was dropped into Ag NPs colloid，the condensation reaction between p-ATP and formaldehyde resulted in the quenching of Raman signals of p-ATP. Thus，formaldehyde was indirectly detected by SERS. Results：Results showed that the method had a good linear relationship in the range of 1.0×10-8-1.0×10-7 mol/L with a correlation coefficient of 0.991 7. The limit of detection was 6.5×10-9 mol/L and the recoveries of formaldehyde were 97.5%~106.0% from the spiked urine samples，which were satisfactory. Conclusion：The method can be applied for the determination of trace formaldehyde in urine with the advantages of less time-consuming，non-preconcentrated procedure and high sensitivity.