Digitalization which has been done in a library is the proof of spreading and implementation of information technology in all fields. National Library of Indonesia (NLI) is also digitizing its collections, mostly of its rare collections. Digitalization is a long process, from collection selection, making a bibliographic document, scanning, file conversion, editing, until file uploading process. Since 2001, there is no further research on this process of the NLI while it is important because NLI is actived in doing digitalization.This research intends to analyze the performance of the digitalization process and evaluates its maturity level using COBIT 4.1. Data that are being used are primary data which are gained from interview for 3 respondents and questionnaires from 8 respondents who are considered as having relevance or understanding IT governance, those who have authority in terms of policy as well as those who directly involved or responsible for digitalization process. Secondary data are also used, such as local and international journal related to digitalization process and COBIT 4.1., planning documents, technical manuals, reports and other documents that are products of NLI.Maturity levels are obtained by mapping the purpose of NLI to the purpose of COBIT 4.1 until mapping of COBIT 4.1?s IT processes. The mapping produce nine of 34 COBIT 4.1?ses IT processes hereafter devised as questionnaire. Questionnaire construction and its calculation is using Maturity Model COBIT 4.1. and Pederiva model.The result value of this research is 2.89 from maturity index of 0-5. It means the level of maturity of digitalization process of NLI is on ?Defined? level. Defined means control is done and is already documented. The management is able to control problems that rarely show up, although the weakness for the control is seldom shown. This is appropriate with interview results that are showing that control on digitalization process is done, there is already monitoring and evaluation although not maximum yet. Quality management and monitoring and IT performance evaluation which have the lowest point 2.73 need to be improved by rescheduling the monitoring and performance evaluation properly and also with adequate human resources in implementation of digitalization process in order to achieve better digitalization process quality and human resource quality. Generally, the performance of the digitalization process is able to meet the goals and objectives of NLI, in accordance with the duties and functiovns for Digital Transformation of NLI.