Veterinary medicines have been widely used for disease protection, growth promotion, and feed efficacy development of animals. Along with development of livestock and pet industry, veterinary medicine market in Korea has increased up to 1 billion US dollar in 2021. The national post-market surveillance (NMS) assessment is important system to manage quality control of veterinary medicines that have reached the open market in Korea. In this study, post marketed veterinary medicines have been analyzed particularly for the active ingredient contents based on the rule, “Tips on animal pharmaceutical audit” and monitored the noncomplicant compounds for prevention of adverse drug event. 6,620 veterinray medicines were chosen by NVRQS-SE10-V1 software program which we developed annually in Korea during 2018-2021. The programe chooses veterinary medicines which is 70% were selected products with high sales in order, 20% were selected products with low sales randomly and 10% were noncompliant product from last year automatically, as we input year`s sales and noncompliant product data. The Animal and Plant Quarantine Agency (APQA) leads collection of veterinary medicines from manufacturing companies, drug stores, and hospitals. The NMS assay was analyzed particularly for the active ingredient ingredients performed using liquid and gas chromatography, titration, UV/Vis spectrophometer, pH, and bioassay in Korea Animal Health Production Association (KAHPA). A total of 129 cases were deemed noncompliant and the average noncompliance rate for veterinray medicines was 1.9%. Among noncompliant products violating regulations, the leading cause was insufficient quantity of major ingredients. The compounds found to be noncompliant most frequently were tylosin, spiramycin, ampicillin, amoxicillin and colistin, respectively In this study, we analyzed the results of post marketing surveillance assay from 2018 to 2021 particularly violation rate and pattern. The overall trend indicated gradually decreasing noncompliance rate from 2.7% to 1.6%, suggesting that the quality of veterinary medicines has improved according to the steadily NMS assay and settlement of Korea Veterinary Good Manufacturing Practice (KVGMP) system.