The critical determinants for e-commerce, e-business, and other enterprise information systems adoption in SMEs have been well-documented. The critical determinants for m-commerce adoption in SMEs, however, are still limited, especially in SMEs in developing countries. This paper develops a measurement instrument for investigating the critical determinants of m-commerce adoption in Vietnamese SMEs. A preliminary study is conducted for confirming the reliability and validity of the instrument based on the data collected from 172 managers of Vietnamese SMEs using an online survey. The Cronbach's alpha and the composite reliability values of the proposed variables strongly support their reliability. The results of the exploratory factor analysis confirm constructs' discriminant validity. The average variance extracted values confirm constructs' convergent validity. This study contributes to the identification of the critical determinants for m-commerce adoption in SMEs. It provides a new conceptual framework for assessing the critical determinants for m-commerce adoption in SMEs in developing countries.