One-dimensional geometric random graphs are constructed by distributing n nodes uniformly and independently on a unit interval and then assigning an undirected edge between any two nodes that have a distance at most rn. These graphs have received much interest and been used in various applications including wireless networks. A threshold of rn for connectivity is known as r * n = ln n n in the literature. In this paper, we prove that a threshold of rn for the absence of isolated node is ln n 2n (i.e., a half of the threshold r * n ). Our result shows there is a gap between thresholds of connectivity and the absence of isolated node in one-dimensional geometric random graphs; in particular, when rn equals c ln n n for a constant c ∈ ( 1 2 , 1), a one-dimensional geometric random graph has no isolated node but is not connected. This gap in onedimensional geometric random graphs is in sharp contrast to the prevalent phenomenon in many other random graphs such as two-dimensional geometric random graphs, Erdős-Rényi graphs, and random intersection graphs, all of which in the asymptotic sense become connected as soon as there is no isolated node.