The research aims to prove the similarity between the processes of grammaticalization of relational nouns into spatial prepositions in Germanic languages of different structure. The paper is original in that it is the first to carry out a comparative analysis of grammaticalization of the English and German nouns ‘side’ and ‘Stelle’ into prepositions with the use of etymological dictionaries. The research results have shown that the process of grammaticalization of these nouns exposed to common ways of grammati-calization is similar and caused by the same grammaticalization mechanisms: desemanticization of original lexical units, decategorialization and phonetic erosion. As a result of grammaticalization of the nouns ‘side’ and ‘Stelle’ (place), the prepositions beside and anstelle von ‘instead of’ have appeared through fusion. It is noted that in the German language, grammaticalization leads to the loss of more grammatical catego-ries (gender, number, case), as the grammatical category of gender does not exist in English. The research proves the role of original meanings of content words in grammaticalization in two languages of different structure belonging to the same language group.