Purpose of the study: Phonological variation in diphthongs, when spoken as a second or foreign language, is an accepted phenomenon. The diphthongs of English when pronounced by native speakers of Pashto go through certain changes and sometimes, monophthised. The purpose of the present study is to investigate phonological variation, i.e., monophthongisation of English diphthongs.
 Methodology: For this purpose, 20 Pashto speakers of both soft and hard dialects were taken and they were asked to pronounce the words having the target diphthongs at initial, medial and final position, followed and preceded by voiced and voiceless sounds. PRAAT was used to analyze the data to measure the possible variations in the sounds.
 Main Findings: The findings show that the phenomenon of monophthongisation of English diphthongs is common in the speaking of native speakers of Pashto. The study further shows that there is the lengthening of some of the sounds and deletion as well in certain contexts. This makes the variety of English spoken by the native speakers of Pashto a separate variety.
 Applications of this study: This study has applications for English language learners and teachers. The learners and teachers of English can benefit from this research and they can work on the problematic diphthongs that are usually monophthised. In this way, these sounds can be practised and the problems can be rectified.
 Novelty/Originality of this study: This is an original study where the problematic diphthongs have been considered and researched that how these English diphthongs are monophthised by the native speakers of Pashto making it a distinctive feature of the native Pashto speakers of English.