The ring opening reactions of propylene oxide (methyloxirane) or ethylene sulfide )thiirane) were studied in the liquid phase over HZSM-5, HY-FAU or AlMCM-41 at 363 K or 423 K and under 1 or 20 bar pressure in a batch reactor. The proportion of these routes were identified: (i) single C−O scission providing non-cyclic products, (ii) double C−O cleavage leading to the loss of the heteroatom, (iii) oligomerisation resulting in cyclic dimers and the trimer of thiirane and a non-cyclic dimer of methyloxirane. The reaction pathway depended on the conditions and the solid acids used. Findings are compared to those in the gas phase over the same solid acids. Transformation mechanisms are also suggested.