This study investigates microstructure evolution of carbonating cement paste under varying water-to-cement ratios (w/c) which is an important parameter impacting initial porosity and pore structure that will in turn influence the carbonation process. Cement samples with different water-to-cement ratios (w/c) ranging from 0.4 to 0.6 were exposed to natural carbonation at 20 ℃ and 65% relative humidity. The microstructure was characterized using MIP and Proton nuclear magnetic resonance relaxometry (1H-NMR). Under saturated conditions, 1H-NMR is able to determine a wider range of pore size distribution from capillary pores to gel pores, and even interlayer spaces typically less than 1 nm. Classical Mercury Intrusion Porosimetry (MIP) is always associated with systematic errors stemming from ink bottle effects, while the external pressure from the device can also induce changes in the microstructure. By applying 1H-NMR these problems can be mitigated, leading to more repeatable results. Results show that NMR offers a more efficient means of monitoring and studying the effects of carbonation on microstructure. Thermogravimetric Analysis (TGA) is also employed to determine the correlation between microstructural changes and carbonation degree.