On most medical drugs, bar codes in the new format "GS1 data bar" are printed on the dispensing package. However, the printing patterns of GS1 data bars vary widely. It is unclear whether bar code scanners are able to scan all types of patterns and also whether all types of scanners are able to scan these patterns. In this study, we present the experimental results of scanning tests of GS1 data bar printed on PTP sheets. As a result, it was found that certain scanners were unable to scan GS1 data bars. Moreover, it was also verified that there were certain patterns of the GS1 data bar that could not be scanned. Factors adversely affecting the quality of scanning were identified such as "existence of a frame," "repetitive printing," "different background color," and "[F] ISO quality grade." Factors advantageously influencing the scanning quality were also identified such as "cost of product is 15,000 yen or more."The printing environment required for GS1 data bars on PTP sheets differs from that for standard bar codes on paper. In this survey, it was found that certain GS1 data bars on PTP sheets could not be scanned. For printing scannable GS1 data bars on PTP sheets, a higher printing quality is required. As GS1 data bars printed on dispensing package units contribute towards pharmaceutical safety management, ensuring accurate scanning is important. For utilizing GS1 data bars effectively, significant effort needs to be made by both the pharmaceutical industry and scanner manufactures.Key words --bar code, GS1 data bar, press through package, dispensing package unit