A study of the in-phase (global, core-wide) and out-of-phase (regional) modes stability analysis with LAPUR5 code for Chinshan NPP(nuclear power plant) is presented. The decay ratios are in acceptable agreement with those from vendor's STAIF code for Chinshan NPP Unit 2 Cycle 22 reloads design. Parametric studies for stability analysis have shown that exposure and control rod position are the most important parameters that might affect decay ratios for in-phase and out-of-phase modes stability analysis. The increase in the exposure causes these effects: (a) the increase in the density reactivity coefficient, (b) the change in the axial power shape from bottom-peaked power shape to top-peaked power shape. Additionally, the change in global decay ratio is depended on the change in density reactivity coefficient and axial power shape, and the regional decay ratio is higher than global decay ratio in the BOC condition and bottom-peaked power shape. The more control rods inserted condition causes the increase in the density reactivity coefficient, global and regional decay ratios.