The article is devoted to the most famous architectural projects of residential, public and religious buildings of Charles Rennie Mackintosh (1868–1928). It is shown that he adhered to the traditions of neo-romanticism, preferred the traditions of Celtic symbolical art, the Scottish folk architecture and the so-called baronial style which make his buildings similar to medieval castles. It is noted that in design solutions and especially organization of internal space of buildings, the architect used the most advanced construction technologies, structures and materials. The article considers six of the most famous architectural projects by Macintosh made in neo-romanticism traditions. Among them, the Lighthouse Tower for the Glasgow Herald (1893–1894), the Glasgow School of Art (1897–1909), Queen's Cross Church in Glasgow (1898–1899), Scotland Street School (1903–1906), the project of the House for an Art lover in Darmstadt (1901), the Нill House in Helensburgh (1902–1904.). The main reasons for the creative crisis of the master on the eve of the I World War are revealed.