A3B5 nanowires are usually grown via the vapor-liquid-solid mechanism. Species from the vapor are incorporated into the nanowires using a catalyst droplet. Typically, the droplet is a low-melting-point eutectic alloy of catalyst and group III metal. This growth imposes a set of limitations on the heterostructure formation and doping. Axial A3B5 heterostructure nanowires obtained via an interchange of group III metals suffer from blurring and kinking. Amphoteric dopants such as Si could act as donors and acceptors, leading to electron-to-hole ratio oscillations along the nanowire. To overcome these limits, the growth with a catalyst, which could dissolve both components of the nanowire, is studied. Tin has a eutectic with both components, As and Ga. This makes the growth of GaAs nanowires with a tin catalyst different from that with standard catalysts. Nanowire growth occurs with at least two types of catalysts, Ga-rich and Ga-poor (As-rich). This article aims to study the nanowire growth with an Sn catalyst. For the first time, the growth of GaAs nanowires using a tin catalyst by molecular beam epitaxy is shown. Tin can serve as a catalyst not only for the chemical growth of GaAs nanowires but also as a nucleation site for their growth. Both compositions of the catalyst are observed. The annealing of a thin film of tin on a Si and GaAs substrate has also been studied. At temperatures below 450 °C, small metal droplets form, while tin dissolves into the substrate at higher temperatures.