Deep ocean floor called as Area is considered as Common Heritage of Mankind (CHM) and the mining activities are managed by International Seabed Authority (ISA). In this article, firstly, the significance of the CHM concept with respect to decolonised states and its impact on law of the sea is elaborated. Secondly, the mandate of ISA which assumed responsibility for the translation of the CHM concept into practice is examined. Every state can take part in mining activities in the Area as a 'sponsor state' but the lack of precision with respect to responsibility limits have a deterrent effect over the states that are disadvantaged technically and financially. Considering the negative impact of this issue over the CHM concept the Advisory Opinion of the International Tribunal for Law of the Sea that was given in 2011 is examined.