While English text readability has been studied for a long time, investigating text readability in Vietnamese, a low-resourced language with poorresearch technologies and data sets questionable of international importance, is at its beginnings. In readability research, it is generally the “word” that has been carefully investigated. Based on the comparison of elements affecting readability of the “word” unit in English, we determine the parts of speech (POS) in Vietnamese that were found to influence Vietnamese text readability. In this study, prose texts in Vietnamese textbooks at different difficulty level were taken as the data to find out the POS frequencies and their correlations. In terms of frequency, our findings can initially assist users when editing documents, reforming textbooks, and question banks for native Vietnamese in general and foreigners in particular. Even more important, with these findings we can identify those linguistic elements that are considered the “potential” POS affecting Vietnamese text readability, and make grounds for further studies.