The objective of this research is to examine the productivity of garment processing using Quick Scan technique in a garment manufacturing plant. Quick Scan Technique is a supply chain diagnostic methodology which collects, and synthesis qualitative and quantitative data form a supply chain and to identify the change management opportunities in the supply chain. The Quick Scan Technique has been pioneered by the Cardiff Logistics System Dynamic Group (LSDG) in collaboration with two of their industrial research partners, enables a heath check to be undertaken on a supply chain to identify and rank areas where improvement would yield most value. To implement the proposed technique, a garment manufacturing plant was selected in Northern Part of Thailand. The manufacturing plant is an OEM manufacturing plant for some leading global clothing brand. One of the main types of product produced by the company is long sleeves shirt, which accumulates to 70% of its production capacity. According to the study, 42 activities were identified and carried out during the production process from fabric inspection till packing. The purpose of the Quick Scan method is to understand and inspect the related raw materials, cost, and resources. In addition, this research identifies the advantages and disadvantages of using the recommended “Quick Hit” for process improvement in applying with the short-term and long-term strategy. Questionnaire data were collected from three main departments namely, marketing, production, and accounting. Statistical techniques were used to analysis and categorize the responses and opinion on supply chain management issues, such as, efficiency, cost, responsibility, reliability, flexibility, quality, and service level. According to the preliminary finding, reliability and cost is considered as one of the most important factors in the supply chain, followed by service with a score of 4.05, 4.01 and 3.81, respectively. Furthermore, production analysis was undertaken in conjunction with Value Stream Mapping (VSM). It was found that several non-value-added activities was presence in the production flow. The application of ECRS (Eliminate, Combine, Rearrange and Simplify) was applied to eliminate and reduce unnecessary process and to re-integrate production flow. VSM was then re-applied to analyse the result of improvement. Finally, the advantages and disadvantages of applying Quick Scan was discussed which offers a new dimension of diagnosing supply chain activities within the garment manufacturing plant in Thailand and ways it can compete with domestic and global market.