The number of the legal regulations is increasing, which implies additional administrative burdens for entrepreneurs. Evaluation of the legal acts efficiency in terms of administrative burdens, is usually conducted after the adoption of provisions. Improvement of existing legislation is a difficult and time-consuming task. Therefore, the aim of conducted research was to develop a method permitting the assessment of administrative burdens in the course of law-making. We propose to apply techniques of business process modelling and reengineering to improve quality of law during law-making. The main contribution of the article is a method based on application of Business Process Model and Notation (BPMN) to design processes introduced by the legal acts. The presented method, due to application of modeling and simulation analysis, permits to precisely assess administrative burdens following from the regulations. The method enables to compare different variants of a legal regulation planned to be established. The presented method was practically applied to the process of registration of a civil law partnership in Poland. It was proved within the conducted research that the process redesigning permits to cut significantly the costs and duration of process both for entrepreneurs and public administration. Due to application of the proposed method the precise data was received, which enabled to compare the costs of burdens in the different variants of the regulations implementation. This case empirically confirmed that application of our method could enhance the quality of public processes regulated by legislation.