PURPOSE: To make catalytic selectivity for a desired product higher by bringing a supply source material into contact with a crystalline porous three-dimensional solid catalyst which is present as a liquid slurry having a reactivity lower than that of the supply source material so as to catalytically convert the source material.

CONSTITUTION: A crystalline porous three-dimensional solid having an ability to promote conversion is compounded in a liquid which is different from the supply source material or the product and which has a reactivity lower than that of the supply source material so as to prepare a catalyst slurry. The supply source material is brought into contact with the catalyst slurry prepared as above described under effective conditions to convert the supply source material into the product so as to obtain the product by catalytic conversion. The supply source material is more soluble in the liquid than the product, and the product is preferably substantially insoluble with the liquid. It is preferable that the liquid to prepare the catalyst slurry contains an effective component such as a base to improve the catalytic activity.