The present invention relates to ethylenically for producing an unsaturated carboxylic acid or ester, or a suitable source of formaldehyde with a carboxylic acid or a reaction catalyst for the ester. The catalyst is two kinds, and include the type or more metal cations M ¹ and a metal oxide having a M ^2, wherein M ¹ is the Periodic Table of the four cycles to 6, a group III belonging to the period or Group 4, of the periodic table 3 cycles to belong to 5 cycles Group 13, or a lanthanum other elements of at least one metal selected from the series, M ² is the periodic Table of the 5 cycles or group V that belong to 6 periods, or the periodic Table of at least one selected from the group 15 belonging to the fourth period or 5 cycles a metal. The invention also relates to a process for the preparation of the ethylenically unsaturated carboxylic acid or ester.