The Clinical Chemistry Subcommittee of the Korean Association for External Quality Assessment Service conducted external quality assessments in 2015. This included general chemistry and blood gas measurements as part of a scheme of six trials, comprising three samples each. All control materials were included at the same time. The overall response rates were 94.4% for general chemistry and 92.2% for blood gas. The parameters tested included sodium, potassium, chloride, blood urea nitrogen, glucose, calcium, phosphorus, uric acid, creatinine, bilirubin, total protein, albumin, total cholesterol, triglyceride, aspartate aminotransferase (AST), alanine transaminase (ALT), alkaline phosphatase, lactate dehydrogenase, gamma glutamyl transferase, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol for general chemistry, and pH, partial pressure of carbon dioxide (pCO₂), and partial pressure of oxygen (pO₂) for blood gas assessments. Two types of reports were generated: a method summary, including mean, standard deviation, and coefficient of variation for each test method; and a result summary of each participating laboratory, including mean, standard deviation, number of peer groups, and standard deviation index and variance index scores of each laboratory. The overall quality performance in 2015 was similar to that of previous years, and showed lower interlaboratory variation than that in 2014. The requisite continual improvement in clinical chemistry testing quality can be achieved through participation in similar proficiency testing programs.