A microporous three-dimensional (3D) hydrogen-bonded organic framework (HOF-20) has been constructed from an aromatic-rich tetratopic carboxylic acid, 5-(2,6-bis(4-carboxyphenyl)pyridin-4-yl)isophthalic acid (H(4)BCPIA). The activated HOF-20a has a moderately high Brunauer-Emmett-Teller (BET) surface area of 1323 m(2) g(-1) and excellent stability in water and HCl aqueous solution. HOF-20 exhibits highly efficient turn-up fluorescent sensing of aniline in water with a detection limit of 2.24 mu M and is selective toward aniline in the presence of aromatic interferents, owing to the hydrogen bonding and edge-to-face p-p stacking interactions between the HOF-20 host and the guest aniline molecules, as demonstrated in the single-crystal X-ray structure of HOF-20.aniline. Density functional theory (DFT) calculations further demonstrate that the recognition of aniline molecules by HOF-20 could restrict the rotation of the aromatic rings in H4BCPIA linkers, reducing the nonradiative decay pathways upon photoexcitation and subsequently enhancing the fluorescence intensity.