This study explores the mixing nature of sodium–indium liquid alloy at temperatures of 713 K, 850 K, 950 K and 1050 K. It uses quasi-lattice approximation for the thermodynamic analysis of concentration dependent mixing behaviours of sodium–indium liquid alloy under the assumption of Na$_3$In complex. It compares the obtained theoretical results with the experimental result and result of Redlich–Kister (R–K) equation for the validity. The researchers concentrate on the viscosity and surface tension of the alloy under the modelling equations as suggested by Kaptay and improved derivation of Butler equation, respectively. This paper focuses on the interaction energy parameters among neighbouring atoms of the alloy. It observes that the alloy is moderately interacting and ordering nature at the lower concentration of sodium. The theoretical results of the thermodynamic properties are nearly in agreement with the corresponding experimental data as well as results obtained by R–K equation at 713 K. It claims that the ordering behaviour, viscosity and surface tension of the alloy decreases with the increase in temperature.