The main goal of this article is to define the problem of vowel duration in Civili (H12a). It shows that the so-called Civili vowel-length desperately needs to be re-examined, because previous works on the sound system of this language hardly explain a number of phonological phenomena, such as vowel lengthening, on the basis of data at hand. Demonstrating the problem in question, the author first reviews previous works that all identify a vowel lengthening in Civili. From different analyses the complexity of the phenomenon is found out by observing differences from an analysis to another, and by regarding difficulties the different phonologists came up against. Then, the problem is also seen through the weakness of each analysis results. This eventually shows more aspects of the vowel duration issue, and leads the author to make a clear distinction between vowel length and vowel lengthening that can be all regarded as only vowel duration. Finally, the article shares a possible way for a solution through an experimental approach of the Civili sound system.