By reducing the pyrrole contents on their surfaces, gold nanoparticles (capped by alkanethiolates and thiolates with pyrrole units) were cross-linked covalently by chemical oxidation into a stable nanoparticle ensemble with chainlike structures. This new and convenient assembly method for gold nanoparticles may be also applied to other functional nanoparticles (e.g., CdS, “core-shell” Co/Pt, and Fe/Au).