Business competition is increasingly complex, and there are no clear boundaries between products, so company operational processes are needed efficiently and effectively. The performance achieved is obtained through the implementation of an integrated information technology known as ERP. ERP implementation requires a person in charge of a business function called a key user who understands business processes and collaborates with ERP system vendors. The study obtained data that can further process from 77 manufacturing companies in East Java by purchasing an ERP or self-development package. Data processing uses PLS to answer all research hypotheses. The results show that key user capability was able to have a direct effect on the effective design of business processes of 0.643 and integration data management of 0.373. In contrast, it had no direct impact on ERP suitability. Effective Design of Business Processes has an immediate effect on Integration Data Management of 0.338 and ERP suitability of 0.395. The results also show that Integration Data Management has a direct effect on ERP suitability of 0.462. The data processing results for the indirect effect showed that key user capability influenced ERP suitability through the effective design of business processes of 0.507. Key user capability affects ERP suitability through Integration Data Management, and it is obtained as much as 0.254. The last hypothesis, key user capability, influences ERP suitability through effective Design of Business Processes and Integration Data Management of 0.182. The study results provide theoretical contributions to ERP implementation success factors, while practical gifts give key users a good understanding of the company's business processes and ERP systems.