Pashto is widely spoken in different regions of Pakistan, Afghanistan, and other countries. Many researchers have studied the Pashto and revealed various interesting aspects of it. However, the purpose of the study is to investigate the use of the morpheme /i:/ as a suffix in Pashto grammar, particularly in nouns (masculine, feminine, singular and plural) and verb. For this purpose, the researchers adopted a qualitative approach and collected data from the native speakers of Pashto. The results of the study showed that the morpheme /i:/ is a very productive process in Pashto in the formation of noun and its plural, and past tense (verb). The results showed that /i:/ cause a morphological change in the root of masculine nouns (e.g., 'zalme' means 'young boy' and 'zalmi:' means 'young boys'), feminine nouns (e.g., 'wana' means 'tree' and 'wani:' means 'trees') and verbs in the past tense (e.g., 'kat̪ ali:’ means ‘saw’). The results revealed that this morpheme brings morphological change to the root of the nouns as well because it adds to the category of the noun ‘χa:n’ meaning ‘king/authoritative person’, and the category remains same (noun) ‘χa:ni:’ means 'wealthy/powerful' and the noun ‘É£ari:b’ means ‘poor’ into the noun ‘É£ari:bi:’ means ‘poverty’.