Owing to the lack of consensus in formal negotiations, unilateral statements do not create legal obligations on states. Thus, a unilateral statement is not considered a source of international law under Article 38 of the Statute of the International Court of Justice. In practice, however, these statements can be legally binding on the states making them and play an important role in the development of international law. The paper aims to examine the characteristics of unilateral declarations and statements in international law and address the Vietnam’s position over the legal effects of the Diplomatic Note 1958 with special references to the South China Sea dispute. This paper will analyze the characteristics and significance of unilateral statements in international law, and argue the conditions for legal binding force. Finally, this paper will provide an in-depth clarification on Vietnamese position on the legal effect of the Diplomatic Note 1958.