This paper presents an adaptive chaotic symbiotic organisms search algorithm (A-CSOS) for finding the solution of optimal reactive power dispatch (ORPD) problem which is one of the main issues of power system planning and operations. The most important advantage of symbiotic organisms search algorithm (SOS) is that is not need any particular algorithm parameters. However, the SOS algorithm has some features to be enhanced, like falling into local minima and sluggish convergence. A-CSOS algorithm with adding new and improved features like adaptivity and chaos to conventional SOS algorithm is proposed to solve ORPD problem. The ORPD problem is mainly focused on minimization of transmission loss (Ploss) and total voltage deviation (TVD). To determine the optimal set points of control variables including generator bus voltages, tap positions of transformers, and reactive power outputs of shunt VAR compensators is very crucial for minimization to Ploss and TVD. The proposed algorithm is implemented on IEEE 30-bus test power systems for ascertaining the performance of A-CSOS algorithm on ORPD problem. The results showed that the proposed approach is up to 10.39% better than many of which the latest algorithms in literature and encourage the researchers to implement A-CSOS algorithm to ORPD problem.