In a study aimed at identifying new anti-prion compounds we screened a library of 500 Australian marine invertebrate derived extracts using a yeast-based anti-prion assay. This resulted in an extract from the subtropical sponge Lamellodysidea cf. chlorea showing potent anti-prion activity. The bioassay-guided investigation of the sponge extract led to the isolation of three new bioactive polyoxygenated steroids, lamellosterols A-C (1-3). These sterols were all isolated in low yield, and their structures elucidated by extensive NMR and MS data analysis. Lamellosterols A-C displayed potent anti-prion activity against the [PSI+] yeast prion (EC50s of 12.7, 13.8, and 9.8 μM, respectively). Lamellosterol A (1) was further shown to bind to the Parkinson's disease implicated amyloid protein, α-synuclein, and to significantly inhibit its aggregation. Our findings indicate that these polyoxygenated sterol sulfates may be useful compounds to study mechanisms associated with neurodegenerative diseases.