The certification of a polystyrene standard reference material, SRM 2888, is described. The Mw of SRM 2888 was determined by light scattering to be 7.19 x 10+3 g/mol with a sample standard deviation of 0.14 x 10+3 g/mol. A combined expanded uncertainty for this light scattering Mw determination, including systematic and random uncertainties, was estimated to be 0.57 x 10+3 g/mol. Mn was determined by NMR analysis of the end groups and found to be 7.05 x 10+3 g/mol with an estimated expanded uncertainty of 0.55 x 10+3 g/mol. Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) were used to analyze end groups on the polymer. The polystyrene was analyzed by MALDI-TOF-MS for the number (Mn) and mass (Mw) average of the molecular mass distribution (MMD) as well as the MMD. The bottle-to-bottle variation of the SRM was checked by size exclusion chromatography (SEC) and found to be negligible.This polymer was also used in an interlaboratory comparison of MALDI-TOF-MS of synthetic polymers. The interlaboratory comparison and its results are described. Agreement between the MMD moments obtained by light scattering and NMR and the moments of the MMD obtained by MALDI in the interlaboratory comparison is found to be good overall. However, all the experimental values obtained by MALDITOF- MS fell below the classical values.