Corpus Taurinense (CT) is the POS tagged version of ItalAnt Corpus, an electronic corpus of Old Italian texts (between 1251 and 1300). In this article we aim to describe the approach followed in CT for the annotation of multiword units (MWU). MWU in our work is a set of two or more graphic words which receive (also) an overall POS tagging because this set of words is in paradigmatic relation with one word lexical unit with the same POS.Our POS tagging confirms that most of the Modern Italian compound conjunctions at that time were not lexicalised. The order of the components is already the Modern Italian order but they can still be interrupted by occasional elements.