As a result of a comprehensive study of the physicochemical properties of the C60-l-cysteine aqueous solutions, practically significant results were obtained, which underlie the understanding of the mechanisms of biological action and biocompatibility. It was shown that the adduct of fullerene C60 with l-cysteine is compatible with water and aqueous solutions and at the same time is amphiphilic. Aqueous solutions are strongly associated and, depending on the concentration, associates of various orders are formed up to the micron size; dilute solutions have high negative partial volumes, which indicate a strong structure. The adduct does not exhibit cytotoxicity, possesses antiradical activity, and reversibly binds to human serum albumin. The obtained data demonstrates the complexity of the systems under study and the prospects for their application in medicinal chemistry and biomedical materials science.