The main aim of the present study is to determine the real practical relevant and volume through the evaulation the United Nations Convention on Contracts for the International Sale of Goods (CISG) and the UNIDROIT Principles of International Commercial Contracts (UPICC). In order to achive the mentioned aims, the study applies the results of the available empirical studies regarding to the CISG, whilst regarding to the UPICC, the study applies the available case law abstracts. In case of the Vienna Convention, it can be obviously stated that, the volume of practical application of the CISG is rather moderate, lags behind the success that the legal literature attributes to it, whilst under the results of revision the available case law in connection with the UPICC, can be declared that, the UNIDROIT Principles mainly promotes the interpretation and completion of the national law and also the international legal instruments, the contracting partie’s intend to apply firstly the UPICC as substantial law, is rather low. Furthermore the study also pay attention the CISG and the UPICC influence to the national law legislation, and declares that, both legal instruments have a huge impact to the national law making.