Organic phototheranostic π-conjugated molecules exhibit great potential for bioimaging and tumor therapy applications due to their well-defined molecular structures, abundant excited state properties, large molar absorption coefficients, and excellent biosafety. However, the strong hydrophobicity of π-conjugated molecules severely restricts their practical applications in organisms. Current research is devoted to using amphiphilic polymer carriers to encapsulate hydrophobic π-conjugated molecules for water dispersion. This may lead to uncontrollable molecular leakage and cause severe liver and spleen enrichment. Synthesis of π-conjugated amphiphilic polymers and construction of one-component micelles have become an emerging strategy for developing phototheranostic materials. In this review, we summarized the recent research progress on one-component phototheranostic nanomaterials based on π-conjugated amphiphilic polymers. First, the category of phototheranostic π-conjugated molecules is introduced. Secondly, the constructions of one-component micelles are discussed in detail. The synthesis of π-conjugated amphiphilic polymers mainly includes the “graft to” and “graft from” methods. Also, the hydrophilic polymers for the synthesis of π-conjugated amphiphilic polymers are classified and discussed, mainly including synthetic polymers, such as polyethylene glycol and zwitterionic polymer, and biological macromolecules, like nucleic acids, peptides, polysaccharides and so on. Finally, the unique properties of these one-component π-conjugated nanomaterials and their applications in regulating molecular assembly, enhancing biocompatible properties, cellular and clinical imaging, and tumor therapy are reviewed. (Figure Presented)