This numerical study is conducted to understand the effect of aspect ratio on heat transfer in rotating Rayleigh-Benard convection (RBC) for Prandtl number Pr = 0.7. The heat transfer characterised by Nusselt number Nu is measured for non-rotating and rotating RBC for Rayleigh number Ra ≤ 5 × 10⁷. For non-rotating RBC, larger Nu is observed for Γ = 2.5 than that for Γ = 1 at low Ra (≲ 10⁵). However, for rotating RBC smaller Nu is observed for Γ = 2.5 than that for Γ = 1 at a given Ra and Ekman number E (Ra ≲ 10⁶ at E = × 10^-4 and Ra ≲ 10⁷ at E = 1 × 10^-4). The opposite trend of Nu with Ra in non-rotating and rotating RBC is attributed to the variation of flow structures. The flow structure inferred from the snapshots of temperature fields in non-rotating RBC shows two convection rolls for Γ = 2.5 and single roll for Γ = 1 . The presence of two convection rolls perhaps leads to more efficient heat transfer than single roll. For rotating RBC, at Γ = 2.5 the flow structures are largely confined to the side walls, widely known as wall modes and the bulk i.e., central region of the RBC cell remains devoid of convection mode of heat transfer leading to the smaller value of Nu than that for Γ = 1. The wall modes scale with the height of the RBC cell. Thus, for Γ = 1 the wall modes significantly intrude into the bulk leading to the larger values of Nu than that for Γ = 2.5.