We utilized scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations to study the diffusion of ammonia (NH3) on anatase TiO2(101). From time-lapsed STM imaging, we observed monomeric and dimeric diffusion channels, and a general tendency to higher diffusion rates with increasing NH3 coverage. In surface regions where several NH3 molecules are adsorbed within a few sites, we further observed the diffusion of NH3 molecules occurring in cascades, where the diffusion of one adsorbate triggers that of others. This eventually leads to apparent diffusion barriers that are lower than expected within a single-jump model. From the DFT calculations, we obtained mechanistic insights into the two observed NH3 diffusion channels. Within the dimeric NH3 diffusion channel, one NH3 swings around another adsorbed NH3 and experiences a reduced diffusion barrier, owing to the intermolecular bonding during the event.