In e-commerce industry, providing good interaction design in organization's online systems is necessary to support organization business. This necessity triggers the ecommerce organization to conduct interaction design process. However, there is no supporting instrument to measure the maturity level of the interaction design process within the organization. This research aims to validate and finalize the proposed interaction design process maturity instrument conducted by expert judgment using Delphi method. Three experts participated in this research by giving their opinion and recommendation based on their knowledge and experiences. The proposed maturity instrument consists of two sections: assessment instrument and maturity level. The level of experts' agreement is calculated using Fleiss Kappa statistic and shown by Kappa value. The result of the expert judgement showed that the expert has 0.74 level of agreement of assessment instrument and 1 level of agreement of maturity level. This level is satisfactory. However, there still some finalization of the proposed instrument, including two indicators' deletion, three indicators' modification, and an indicator addition. There are also minor modifications for the proposed maturity level.