A protein sequencer is a machine that is used to determine the sequence of amino acids in a protein.

They work by tagging and removing one amino acid at a time (how? by chemicals? what are these chemicals designed to do), which is analysed and identified. This is done repetitively for the whole polypeptide, until the whole sequence is established.

This method has generally been replaced by nucleic acid technology, and it is often easier to identify the sequence of a protein by looking at the DNA that codes for it.