Recent earthquakes in Myanmar have underlined the need for wide monitoring and safety assessment of cultural heritage structures. The study presents the seismic vulnerability evaluation and seismic strengthening of a specific monumental masonry structure: the main stupa of Kuthodaw Pagoda in Mandalay. The required experimental tests were conducted to determine the material properties of the structure. The probabilistic seismic hazard analysis was done to get ground motion data consistent with local seismic conditions. These seismic waves were used for the input of time history analyses. Comparisons of the expected seismic demand and the capacity of the structure were done to determine the weak parts of the structure under earthquakes. The fragility curves of the structure under consideration with and without external steel rings were developed. The results have shown that the use of external steel rings can significantly reduce seismic vulnerability and effectively strengthen the structure against earthquake.