Specific receptors are required for the autophagic degradation of endoplasmic reticulum (ER), known as ER-phagy. However, little is known about how the ER is remodeled and separated for packaging into autophagosomes. We developed two ER-phagy-specific reporter systems and found that Atlastins are key positive effectors and also targets of ER-phagy. Atlastins are ER-resident GTPases involved in ER membrane morphology, and Atlastin-depleted cells have decreased ER-phagy under starvation conditions. Atlastin's role in ER-phagy requires a functional GTPase domain and proper ER localization, both of which are also involved in ER architecture. The three Atlastin family members functionally compensate for one another during ER-phagy and may form heteromeric complexes with one another. We further find that Atlastins act downstream of the FAM134B ER-phagy receptor, such that depletion of Atlastins represses ER-autophagy induced by the overexpression of FAM134B. We propose that during ER-phagy, Atlastins remodel ER membrane to separate pieces of FAM134B-marked ER for efficient autophagosomal engulfment.