Axons contain an endoplasmic reticulum (ER) network that is largely smooth and tubular, thought to be continuous with ER throughout the neuron, and distinct in form and function from rough ER; the mechanisms that form this continuous network in axons are not well understood. Many mutations for the axon degenerative disease, hereditary spastic paraplegia, affect ER-shaping proteins. Here we test whether these proteins are required for modeling the axonal ER network in Drosophila. Loss of Rtnl1 or REEP proteins can lead to expansion of ER sheets, and to partial loss of ER from distal motor axons. Ultrastructural analysis reveals an extensive ER network in every axon of peripheral nerves, that is reduced in larvae that lack Rtnl1 and both REEPs, with defects including larger and fewer tubules, and occasional gaps in the ER network, consistent with loss of membrane curvature. Therefore HSP hairpin-containing proteins are required for shaping and continuity of the axonal ER network, and their mutant phenotypes may have consequences for axonal physiology.