The objective of the present work is to characterise, using an experimental microscopic observation device, the crystal size distribution (CSD) of ice and tetrahydrofuran (THF) hydrate slurries, which can be used as two-phase refrigerant fluids for cold transportation and storage in the field of secondary refrigeration. Three different solutes (ethanol, propylene glycol and sodium chloride) were used to form ice slurries. The studied hydrate was THF hydrate since it is stable at atmospheric pressure and in a temperature range suitable for refrigeration and air-conditioning applications. Experimental ice and THF hydrate slurry CSDs were compared to classical normal (Gaussian), log-normal, gamma, and Weibull (RosinRammler) distributions. A comparison between ice and THF hydrate slurry CSD results showed that hydrate slurries were composed of crystals approximately 1.5 times smaller than ice crystals. The present results were shown to be useful input parameters for modelling thermophysical properties of slurry systems.