jats:titleAbstract</jats:title>jats:pSurface coating is a powerful approach to fabricate multifunctional materials that are essential for numerous applications. However, to achieve such multifunctional coating with a facile single‐step procedure, especially on flexible substrates, is still a big challenge, as current fabrication protocols usually require sophisticated equipment and complicated procedures. Here, a novel coating technology involving in situ self‐assembly of the polyoxotitanate (POT) cage [Tijats:sub18</jats:sub>Mnjats:sub4</jats:sub>Ojats:sub30</jats:sub>(OEt)jats:sub20</jats:sub>Phenjats:sub3</jats:sub>] is reported to fabricate multifunctional cotton fabrics in a single step. The in situ generated spherical microparticles of 0.8 µm average diameter are firmly mounted on the underlying cotton substrate, imparting the coated surface with robust hydrophobicity (water contact angle of 148.1 ± 5.4°), antibacterial activity (against jats:italicEscherichia coli</jats:italic>, jats:italicStaphylococcus epidermidis</jats:italic>, and jats:italicStaphylococcus aureus</jats:italic>), and excellent UV‐blocking performance (89% blocked at 350 nm). This coating technology is efficient, straightforward, requires no specialized equipment, and most importantly, is readily extendable to other flexible substrates. Combined with the rapidly developing area of POT cages and similar molecular materials, the reported technology based on in situ self‐assembly holds great promise for further advancing the fabrication of multifunctional flexible devices via a single‐step coating operation.</jats:p>