In this study, we evaluated the chemical chaperone activity of synthetic 4-phenylbutyric acid (4-PBA) derivatives. These derivatives have a methoxy group at the benzene ring and/or longer or shorter fatty acid portions. Several 4-PBA derivatives demonstrated higher antiaggregation activity than 4-PBA. Moreover, 4-(4-methoxyphenyl)butanoic acid (7b) showed protective effects against endoplasmic reticulum stress-induced neuronal cell death.