This paper presents a new study on the prosody of Vietnamese language. Sentence pairs containing one interrogative sentence and one affirmative sentence, which have the same tones and the same number of syllables to avoid the effects of lexical tones and of co-articulation, are recorded in order to analyze their prosody evolution. Comparisons allow us to characterize differences between interrogative and affirmative sentences at sentence prosody level. Our work is completed by a perceptual study on re-synthesized sound where all syllables of the sentence are replaced by the vowel /a/ to hide lexical meaning, while the prosody of the sentence is kept unchanged. Our goal is to see if sentence prosody carries any information about sentence nature characteristics, and then whether it enables listeners to classify sentence type (in this case interrogative and affirmative), despite the complex form of this prosody in tonal languages. The obtained results show that information on sentence type is present at the end of the second half of the last syllable and that about 70% of sentences are properly classified for female synthesis voice.