The nPVI measurement is an empirical tool used for finding phonetics evidence supporting language classification in terms of rhythmic properties. The nPVI can also be used in order to find the influence of a composer's native language on instrumental music's rhythm (Patel and Daniel, 2003). However, there is a question as to whether music with lyrics will yield the same result as instrumental music. Therefore, this study aims to investigate rhythm in Standard Thai and Northern Thai pop songs. The results show that the nPVI value for Standard Thai pop songs is lower than the nPVI value of Northern Thai pop songs and the result of rhythmic property in music obtained from nPVI calculating is not parallel with speech nPVI value. To illustrate, musical nPVI value calculated from Standard Thai pop songs is lower than the musical nPVI value of Northern Thai pop songs. This incongruousness might result from the influence of Western music and melodies on Standard Thai pop songs and folk melodies on Northern Thai pop songs.