A biocompatible material having excellent biocompatibility such as small interaction with a component of a living body such as a protein or blood cell. A biocompatible material comprising a polymer obtained by polymerizing a monomer composition comprising an amino acid-type betaine monomer represented by the formula (I): ##STR00001## wherein R.sup.1 is a hydrogen atom or a methyl group; R.sup.2 is an alkylene group having 1 to 6 carbon atoms; each of R.sup.3 and R.sup.4 is independently an alkyl group having 1 to 4 carbon atoms; R.sup.5 is an alkylene group having 1 to 4 carbon atoms; and Z is an oxygen atom or an --NH group; and a polymerizable monomer represented by the formula (II): ##STR00002## wherein R.sup.1 is as defined above; and R.sup.6 is a monovalent organic group, in a weight ratio, i.e. amino acid-type betaine monomer/polymerizable monomer, of from 1/99 to 100/1. The biocompatible material can be suitably used, for example, in food, a food additive, a medicament, a quasi-drug, a medical device, cosmetics, a toiletry article, or the like.