Composite floor systems using light gauge steel sheeting are gaining reputation worldwide. These composite slabs contribute to faster, lighter and economical construction of buildings. With lightweight aggregate concrete, the composite deck slabs offer henceforth new assets such as higher unpropped span during construction, supplementary reduction of self weight of the floor (up to 40% compared to the normal concrete), lasting heat insulation, etc. However, the longitudinal shear behaviour of composite deck slab must be studied by experimental methods to justify the combination of the steel deck and lightweight concrete and to evaluate the m-k values as defined by EN 1994-1-1. This paper presents a complete experimental investigation conducted on the lightweight composite deck slabs associating steel deck and pumpable lightweight concrete.