Based on partial studies along with archival and newspaper sources, the author aimedto analyse the emergence (and fall) of the idea regarding the Czechoslovakian-Yugoslav corridor before and after World War I as well as at the Paris Peace Conference. The idea of a territorial connection between both countries was formed during World War I in the heads of intellectuals, one of whom was the Czech professor Tomaš G. Masaryk, who played an important role in the process. The genesis of this project remains vague, the idea was most probably formed in the scope of plans of the Slavic federation (Karel Kramar). The corridor was planned in the Western part of Transdanubia, running along three Hungarian administrative units, i.e. counties. The idea had been “maturing” during the war on both sides until it was ultimately rejected by the Paris Peace Conference.