(Calcein-ZnS)(n) ultrathin films (UTFs) were fabricated through a two-step procedure including the layer-by-layer (LBL) assembly of calcein and exfoliated Zn2Al layered double hydroxide (LDH) nanosheets, followed by an in situ gas/solid reaction with H2S. The assembly process of calcein and exfoliated LDH was monitored by UV-vis absorption measurements to get a stepwise and regular growth of the (calcein-LDH)(n) UTFs upon increasing the deposited cycles. By an in situ gas-solid reaction with H2S, the resulting sulfurization derivatives denoted as (calcein-ZnS)(n) UTFs were obtained. The resulting (calcein-ZnS)(30) UTF possesses high ethanol sensing performance (response value is 8.9-100 ppm ethanol) at relatively low working temperature (90 degrees C). The LBL assembly process and chemical conversion technique based on Zn2Al-LDH combine the functional organic molecules and inorganic semiconductor, which enables us to develop innovative composite materials with adjustable compositions for a broad range of applications.