Molten　salts　and　their　mixtures　are　widely　used　as　heat　transfer　fluid　in　the　research　area　of　solar　energy　applications.　Measured　viscosities　of　molten　salts　often　show　large　discrepancies　due　to　difficulties　of　measurement　at　elevated　temperatures,　especially　for　molten　salt　mixtures.　In　this　paper,　a　theoretical　model　is　presented　for　predicting　the　viscosity　of　binary　molten　salts,　in　which　only　data　of　viscosity,　density　and　fraction　of　each　component　salt　are　needed.　Comparisons　with　experimental　data　show　that　the　model　gives　prediction　of　viscosity　with　errors　less　than　9.94%,　though　part　of　this　error　may　probably　come　from　experiment.　In　comparison,　the　Eyring　equation　always　gives　larger　errors,　reaching　11.4%　in　the　worst　case.　The　present　work　indicates　that　the　model　shows　improved　ability　in　prediction　of　viscosity　of　molten　salt　mixtures.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.