Certified reference materials (CRMs) are playing an increasingly important role in national and international standardizing activities. In Japan, primary standard solutions for analyses of endocrine disrupters are supplied under the national standards dissemination system named the Japan Calibration Service System (JCSS). For the traceability on reference materials used for preparation of the primary standard solutions based on the JCSS, the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) has developed and certified high-purity reference materials of alkylphenols as NMIJ CRMs, such as 4-n-nonylphenol, 4-tert-octylphenol, 4-n-heptylphenol, 4-tert-butylphenol, and 2,4-dichlorophenol. Thereafter, it is essential to determine the alkylphenols by using these solutions based on the JCSS for environmental monitoring and risk assessments because analytical values obtained by using the solutions can ensure the reliability and traceability of the chemical analyses.