The article is an attempt to underline the difference in the conduct of foreign policy by two allied countries. One of them – France, had the opinion of the most powerful state in Europe after World War I, and the other – Belgium, was a small country that decided to abandon its neutrality (imposed by the great powers in 1839). Such an alliance, salutary for strengthening the security guarantees towards the former occupant, brought with it fears of domination and instrumental treatment. In matters of eastern policy, both countries were concerned about the loss of numerous investments and capital investments in tsarist Russia. It was through this prism that the Polish-Bolshevik war was assessed. The second factor that distinguished the two countries in their approach to the war was the different composition of the government. While in France the electoral victory of the National Bloc facilitated the conduct of politics, the government of catholic-socialist coalition in Belgium faced serious obstacles from the socialists, which was manifested in the decision concerning the transit of weapons to Poland. French aid in the form of weapons supplies and support for Poland from the diplomatic side led to an alliance with Poland. Belgium took advantage of the end of the war to establish, above all, economic cooperation.