Intermetallic ternary nanoalloys (NA) have increasingly gained prominence as excellent catalysts. But, their size, morphology and chemical compositions affect their catalytic and interfacial activities significantly. In this study, we present laser-induced breakdown spectroscopy (LIBS) for rapid quantitative elemental composition characterization of ternary NAs with different elemental ratios. Specifically, we use a calibration-free approach with LIBS to estimate the elemental ratios of PtCuCo ternary NAs with various stoichiometric ratios synthesized via our in-house laser ablation synthesis in solution-galvanic replacement reactions (LASiS-GRR) technique. The size and morphology of the samples are determined from transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) measurements. The LIBS quantitative estimations for the NA samples are compared with results from inductively coupled plasma-optical emission spectroscopy (ICP-OES). The elemental ratio results of quantitative LIBS show good agreement with ICP-OES results, while being devoid of any external standard requirements or extensive sample preparations.