Liquid marble is a non-wetting droplet encapsulated by micro- or nano-sized hydrophobic particles. Recently, liquid marble has been emerging as a tool for digital microfluidics. Thus, a detailed understanding of the fundamentals of liquid marble is essential. The shell of a liquid marble has an opaque and fuzzy appearance which hinders in-depth investigation using conventional optical microscopy. We used X-ray computerized microtomography (CMT) to generate an image with a visible interface between the core liquid and the shell to overcome this problem. The interface facilitates accurate measurement of the shell thickness and the effective surface tension. This work investigates the effect of liquid marble preparation methods and liquid marble volumes on shell thickness and effective surface tension. We found that increasing the revolution speed during liquid marble preparation increases shell thickness. A liquid marble shell has a uniform packing when the revolution speed is 200–300 rpm. We also found that the effective surface tension of liquid marbles decreases with increasing volume. This could be due to a stronger effect of gravitational force for a large liquid marble. The findings from this work could provide a new insight into the characterization of liquid marble and open up a new direction of fundamental research of liquid marble shell.