Mesoscale convective systems (MCSs) account for nearly half of the total precipitation over the tropics, playing an essential role in the tropical hydroclimate. However, its initiation and the thermodynamic states associated with its life cycle remain unclear, which sets the challenging representation of MCSs and related processes in global high-resolution models. A measure of lower-tropospheric buoyancy that accounts for a combination of instability and entrainment has provided baseline empirical buoyancy-precipitation relationships for deep convection. Here we characterize such relationships during the evolution of MCSs, aiming to pin down an observational benchmark for MCS-related thermodynamics. The Feng (2023)  20-year MCS dataset from a satellite-based, global MCS tracking algorithm (FLEXTRKR; Feng et al, 2021) is used for MCS properties combined with GPM-IMERG precipitation, with ERA-5 reanalysis used for thermodynamic variables required to calculate the buoyancy measure. MCS lifecycle is separated into initiation, growing, mature, decaying, and end phases. The preliminary results indicate that the evolution of MCSs initiates at high instability and lower saturation, moves towards low instability and high saturation at the mature phase, and ends with much lower instability and saturation than at its initial stage. A buoyancy-precipitation relationship suggests that a higher probability of high-end buoyancy is revealed in MCSs at the growing and mature phase, with a considerable contribution to conditional precipitation. At lower buoyancy, the relative precipitation contribution from the decaying phase of MCSs becomes greater. These qualitative characteristics are consistent between MCSs developing over oceans and land. The conditional precipitation rate as a function of the thermodynamic buoyancy measure is observed to have a dependence on the lifecycle phase, which provides constraints on the overall time dependence of the precipitation process associated with microphysics and dynamics in MCS evolution.