Independent audit assurance of sustainability reporting is the basis for increasing the credibility of the stakeholders, its transparency and reliability; it is a means of implementing legal liability of the company and the evidence of achievement of its legitimacy to the public. The bases for providing such assurance are the standards of implementation of audit tasks in the sphere of sustainable development. Comparative analysis of international practice as for assurance regarding the SR with local realities, based on the reporting database of Ukrainian GRI companies for the 2005-2014 years, witnessed the initial phase of such practices among Ukrainian companies, and the need to strengthen regulatory efforts to determine the legal status of SR auditing standards in Ukraine, ensuring a legal environment and the development of corporate social responsibility initiatives.