The main purpose of this paper is to study the difference between Articles 73(1) and 51(1) and draw a significant practical note for the parties. In order to accomplish these goals the core contents of Articles 51 and 73 will be reviewed and comparative analysis will be done. To begin with, if both rules are applied for the same situation concurrently it is easy for the parties to use the Article 51 for the avoidance of contract because parties have to prove the occurrence of fundamental breach under Article 73. It is not easy to prove the existence of the fundamental breach of contract. Second, Article 73 does not expressly provide for a period within which the avoidance should be declared. An implicit time limit for the exercise of a right of avoidance can be read into Article 26. This time limit can be applied also under Article 73(1). But there are so many disputes on this issue. It is desirable that the parties should set a time limit for the exercise of a right of avoidance. Third, there is no procedure for avoiding a contract, in case of non- fundamental breach, on the ground of the breaching party's failure to perform after being given an additional period of time under Article 73. But Article 47 have been applied under Article 51. Thus, it is desirable that parties come to an agreement for the additional period of time to perform their obligations. CISG Articles 51 and 73 are often considered concurrently as they both deal with the scenario where only part of a contract has bee performed. But there are some difference between the two Articles. Therefore, parties have to note the common things and differences between the two Articles and use the two rules in order to enlarge the both parties benefit.