Abstract: To assess human exposure to harmful aerosols it is desirable to sample the aerosol fraction which is directly involved in the biological mechanism. The concept of health-related aerosol fraction was first proposed in occupational health and used for size-selective sampling at workplaces. The BMRC (British Medical Research Council) definition of respirable aerosol particle fraction was recognized internationally in 1960. It was worth noting that a definition of three health related aerosol fractions (inhalable, thoracic and respirable) was adopted consistently by European Committee for Standardization (CEN), International Standards Organization (ISO) and American Conference of Governmental Industrial Hygienists (ACGIH) in the 1990s. The definition of respirable dust was introduced into China formally as the occupational limit in 2002. In recent years ultrafine particulates were proposed. Because of their small size (nominal diameter ≤ 100 nm), thereby getting in and out of cells easily, these particles posed a great health concern. A draft was formulated by ISO/CEN in 2004 to assess the occupational exposure of ultrafine particles. Recently a new convention for aerosol particle sampling was proposed by Bartley, which included 5 specific areas of respiratory tract rather than the traditional 3 regions for deposition, ultrafine aerosol particles also, and an array of 7 samplers with different thermodynamic and aerodynamic principles for measurement. However, it was not intended to replace the current international standards, but to promote the design of samplers. Based on Bartley's review and relevant information, some progress on aerosol definition and sampling strategy is briefly introduced in this paper to arouse the attention of our fellows.