The article examines the evolution of Franco-Spanish relations in the late XVIII – early XIX centuries. The subject of the study is the peculiarities of the development of relations between France and Spain, the analysis of various factors that influenced the diplomacy of the two countries. The object of the study is various treaties, armed conflicts and specific political steps characterizing Franco-Spanish relations. Special attention is paid to the role of the union of the two countries in the confrontation with Great Britain. The purpose of the study is to analyze the causes and consequences of changes in relations between France and Spain in the late XVIII – early XIX centuries. A special role in the evolution of Franco-Spanish relations is noted for the coup d'état of 18 Brumaire in France and the rise to power of Napoleon Bonaparte. The active foreign policy of Napoleonic France eventually resulted in a full-scale war on the Iberian Peninsula. The author uses chronological, historical-comparative and historical-systemic research methods in his work. These methods allowed to analyze the evolution of the Franco-Spanish relations in the late XVIII - early XIX centuries. Periods of military confrontation were interspersed with the time of the union of the two countries. There was a certain duality at the heart of the Franco-Spanish alliance. On an ideological level, most of Spanish society did not accept the ideas of the French Revolution. From an economic point of view, it was not profitable for Spain to enter into the Anglo-French confrontation. Ties with the Spanish colonies were disrupted. From the point of view of European politics, Spain, isolated by its geographical location, did not always benefit from an alliance with France, since it was an unequal partner in it. A special contribution of the author to the study of the topic is the proposed periodization of the history of Franco-Spanish relations of the late XVIII – early XIX centuries, its division into a number of stages. This makes it possible to better structure the work and identify the interrelationship of the changes that determined the nature of Franco-Spanish relations at each stage. The novelty of the research lies in the fact that in this work the evolution of Franco-Spanish relations in the late XVIII – early XIX centuries is considered as a whole and continuous process, the influence of domestic political events on changes in the foreign policy of the two countries is analyzed.