This invention relates to a method of preparing a preform for an optical fibre, and more particularly to a method of preparing a preform for a polymer holey optical fibre. The invention provides a method of preparing a preform for manufacture of a polymer holey optical fibre comprising casting a preform body in a mould from a suitable material, said mould including at least one protrusion adapted to form a corresponding hole within the preform, and subsequently separating the preform body and mould. The invention also provides a method of preparing a preform for manufacture of a polymeric holey optical fibre comprising separately casting one or more elements of a preform in respective mould(s) from a suitable material, and separating said elements from said respective mould(s) and combining said elements to construct a preform having a plurality of holes therein, each hole being formed in an element or formed by the combination of two or more elements.