The GB/T 1545-2008 standard specifies the determination method of acidity or alkalinity of paper, Cardboard and pulp aqueous extracts. The standard refers to the international standard ISO 6588:1986 and mainly updates the standard name, scope, definition of terms and test procedures. The standard includes two determination methods: Titrimetric method and pH Meter method. Titrimetric method is suitable for the determination of acid alkalinity of general paper products, while pH Meter method is suitable for samples with conductivity exceeding 0.2 mS/m. The standard specifies in detail the reagent preparation, sample handling and instrumentation requirements, and clarifies the determination steps. This standard replaces both GB/T 1545.1-2003 and GB/T 1545.2-2003 and adds a description of comparisons and technical differences to the ISO 6588:1986 standard.