The microstructure of vapour grown carbon fibres is two-double layered. This paper addresses the question of morphology transformation of vapour grown carbon fibres. Special attention is given to developing understanding of the growth mechanism of the outer layer of the fibres. The influence of growth time on the morphologies of as-prepared carbon fibres was investigated using scanning electron microscopy. Results showed that with the prolongation of reaction time, their morphology changed from linear fibres to carbon micro-bead chains and then again to thicker linear fibres, which led to the increase of the carbon fibres diameters from 200 nm to several micrometers. Furthermore, several kinds of carbon fibres with special morphology such as carbon micro-beads, chains, etc., could be obtained by adjusting the growth time. A growth mechanism, henceforth referred to as fibre-bead-thicker fibre, for the outer layer of vapour grown carbon fibres is proposed.