Diet strongly influences the chemistry of vertebrate soft and hard tissues. Bird bone and eggshell mineral preserve reliable records of prey consumption, even beyond the life of the predator, and analyses of hard tissues have usefully reconstructed avian diet. Here, we assess the feasibility of a non-destructive method for distinguishing krill-poor from krill-rich diets in penguins. Krill (Euphausiaceae) are fluoride-rich, and penguins that consume krill produce fluoride-rich bones. The chemistry of bone mineral may be elucidated using Raman spectroscopy without recourse to specialised sample preparation. Published data from the diet of six penguin species were compared to a fluoride-informative spectral band (phosphate symmetric stretch, ν1-PO43−) in the Raman spectra of penguin humeri. Penguins that consume abundant krill (e.g. Adélie and emperor) have ν1-PO43−-band positions higher than 963 cm−1, whereas penguins that primarily eat teleost fish or cephalopods (e.g. Fiordland crested, Humboldt, little blue and yellow-eyed) have ν1-PO43−-band positions lower than 963 cm−1. A krill-rich diet can therefore be determined from the Raman spectra of penguin bones. Raman spectroscopy could be a useful supplement to existing diet analysis techniques.