Abstract: In order to offer guidance on correctly using certified reference materials (CRMs) of 16 polycyclic aromatic compounds (PAHs) in methanol (named PPH10RPM) manufactured by ChemService Co. Ltd in application of PAHs analysis, stability of CRMs in opened stocks was tested by gas chromatography with a flame ionization detector (GC/FID). The CRM was transferred into 2 mL brown bottles equipped with Teflonlined screwcaps, stored with minimal headspace and protected from light at -18℃ for 123 days. The variation of property values of the CRMs with storage time was determined. The results showed that the standard deviations of all the property values ranged from 0.3~4.0 μg/mL and the maximum relative standard deviation was 3.92%. In the 95% confidence level, the chisquared test (χ2-test) showed that precision of the measurements was acceptable and indicated the evaluation method was feasible and reliable. In addition, the measurement deviation was not significant when the range of property values of the CRMs were within (100.0±7.2) μg/mL. The experiment data also showed that the preservation period of the CRMs for opened stocks was up to 80 days and the period of validity of the CRMs should be considered.