The effects of several quaternary ammonium compounds on electrodeposition of zinc onto AISI 1018 carbon steel were studied in an alkaline zincate electrolyte. Tetraethylammonium, tetrabutylammonium, N-benzyltriethylammonium and N-benzyl-3-carboxyl pyridinium cations were examined. The electrochemical behavior and the inhibition of dendrite formation are related to the structure of the ammonium compounds. The presence of either long-chain aliphatic groups or aromatic groups, i.e., with tetrabutylammonium hydroxide (TBAOH) or N-benzyltriethylammonium chloride (NBT) exerts a more effective inhibition of dendrite formation. N-benzyl-3-carboxylpyridinium (3NCP) and tetraethylammonium hydroxide (TEAOH) additives lead to slightly deformed deposit morphology. Crystallographic measurements of the zinc deposits revealed a highly oriented deposit formed in the presence of 3NCP, which favors the dense atomic packing basal plane (002). The presence of TEAOH diminishes slightly the peak of plane (002) and introduces some pyramidal (101) orientation. Addition of NBT or TBAOH favors the formation of low-atomic packing prismatic planes. Additives that increase the overpotential for Zn(II) reduction tend to promote the formation of high-energy low-atomic packing crystallographic planes. Comparison of the effects of these ammonium compounds indicates that the observed effects are related to the hydrophobic and steric interactions introduced to the interface by the size and structure of the ammonium compounds.