Recently, utilizing the supply chain among companies, major companies support their sub-vendors to establish an environmental management system and transfer the clean production technology(know-how) to them for strengthening of environmental competitiveness. Thus, Green Supply Chain Management(GSCM) became a key successful factor for companies to be environmentally sustainable. This research endeavors to identify the relationship among the inside and outside GSCM implementation activities of Korean manufacturing companies and their financial, operational and environmental performances. Based on a the review of previous research findings, twenty one hypotheses are developed and examined. Total 251 valid responses from 1,634 survey responses are identified and the structural equation models(SEM) are developed and analysed for examining our hypotheses. The result shows that inside GSCM has a positive effect on outside GSCM. Also, it reveals that companies’ performances are more positively affected by inside GSCM than by outside GSCM.