In this paper a method for online Transient Stability Analysis/assessment (TSA) of large scale power systems is proposed. The method is based on an exact mathematical transformation of (n+m)-machine system into n-equivalent single machine-to equivalent bus (SMEB) models, and m-load to-equivalent bus (LEB) models, where n number of machine buses and m number of load buses in the system. Then implementing proposed Parallel Algorithms (PAs) for power system TSA on developed MATLAB/M-files models constructed by the authors for system simulation. Comparative simulation results between the proposed PAs and Conventional Time Domain Method (CTDM) are presented to show the effectiveness and the validation of the proposed PAs.