Purpose : This study has analysed empirically the effect of service quality of platform companies on management performance, the effect of brand value and brand reliability as medium factors on management performance, in accordance with rapid growth of B2C e-commerce in the Post-Covid era. On that basis, the study intended to propose the importance of service quality of the management performance improvement and competitiveness reinforcement of B2C e-commerce platform companies. Research design, data, methodology : The questionnaire target of this study has designated the persons interested and general using customers of B2C platform company and conducted the questionnaire survey. For the analysis, SPSS 26.0 and AMOS 26.0 are used and executed. Results : Through this study, the analysis result which was summarized is as follows. first, if service quality (security, responsiveness, efficiency, empathy) as independent factors improved more, the effects on the management performance as subordinate factors all turned out to have significance. second, if the responsiveness, empathy and brand value as service quality was higher, the effect on the management performance confirmed to have significance. third, if seeing the result of effect of service quality with medium factor such as brand quality on management performance, service quality(security, responsiveness, efficiency, empathy) was confirmed to have significant influence on the management performance through brand reliability. Conclusions : This study has presented improvement strategy of the service quality for the maximization of competitiveness improvement and management performance of B2C Platform companies. In the future, it is anticipated to be fundamental study on the service quality.