This article is an acoustic analysis of the Maithili diphthongs. The article attempts to analyze topics such as the possible difference of the perceived diphthong from the perception of a pair of vowels. With the help of some attributes gathered from the results of a spectrographic study of the Maithili diphthongs, the article concludes that the phonetic features emerging from the consideration of diphthongs in a particular language are not necessarily sufficient or optimal to characterize the phenomenon in general. The most significant attributes of the Maithili diphthongs are two: (i) their onset frequency position and (ii) their second-format rate of change, which is always very stable in these diphthongs across changes in duration conditions. (Rajeev Ranjan Singh 2007-01-31)