Materiality-approaches to sustainability reporting have been developed and adopted in some businesses in recent years, and proved in practical terms an important advancement on reporting methods, by tackling or lessening some key problems in stakeholder-approaches. What is ‘sustainability materiality’? Are there any difference between sustainability materiality and financial materiality? How application of materiality would meet the challenges that confront traditional stakeholder-approach reporting? And furthermore, can materiality provide an absolute solution to sustainability reporting? If not, how to improve it? Part one tries to answer these questions in a critical look, and to provide a further view on “New Challenges” to ‘sustainability materiality’ –interrelationship and subjectivity. Part two is a case study on ‘sustainability interrelationship’ and ‘stakeholder relevance’. It is the preliminary study on the challenge to sustainability materiality.