| This Research has an objective to discover end user satisfaction level of Electronic Collaborating System (ECS) and the relationship between individual work performance at Big Five Public Accountant Firm. This Research use End User Satisfaction Theory and Individual work performance indicator. The Subject of this research is an auditor who working or have already worked in Big Five Public Accountant Firm and had used ECS. Analysis techniques that use for this research is Partial Least Square (PLS) with the help of SmartPLS 3.0. Data that has been collected was 100 and all of them valid to be use. There is two conclusion in this research. First, end user qiute satisfaction with ECS. Second, end user satisfaction has a positive relationship with individual work performance |