ABSTRACT: Stack bonded masonry is a form of construction in which the masonry units in adjacent courses are aligned vertically above one another. This bonding pattern leads to continuous vertical joints running the full height of the wall resulting in a weak form of construction, particularly under horizontal out-of-plane bending. For this reason, the use of stack bonded masonry in Australia is not encouraged and design provisions in the Australian masonry structures code AS3700 (Standards Australia 2011) predict zero strength in horizontal bending for unreinforced stack bonded masonry. However, stack bonded masonry is increasingly being specified in designs for architectural effect, and in these cases, specific structural design requirements are needed. This paper presents experimental results on the performance of typical Australian stack bonded clay brick masonry subjected to one way horizontal bending under lateral out-of-plane pressure loading. The study considers unreinforced running bond (control) specimens and stack bonded specimens with zero and three levels of stainless steel bed joint reinforcement. It was found that while unreinforced stack bonded masonry has very low horizontal bending strength, the presence of bed joint reinforcement is highly effective in improving both the strength and ductility of the masonry. Furthermore, the performance improves with increases in the reinforcement percentage and the provisions of AS3700 for reinforced masonry were shown to accurately predict the strength of the reinforced specimens.