This work is devoted to the analysis of the dynamics of the sentiments of soldiers drafted from the Olonets province in letters to their loved ones during the First World War. The purpose of the study is to show how the moods of military personnel changed from the beginning to the end of the war. The material consisted of letters from soldiers from the Olonets province, published in the collection of some documents of the National Archive of the Republic of Karelia and the Leningrad Regional State Archive “Karelia during the First World War: a collection of documents and materials”. The methodological complex includes such methods as the historical and systematic method, the historiographic method, the synthesis method, etc. An analysis of the epistolary work of the soldiers of the Olonets province, called up to the front, showed that the dynamics of the tonality of front-line letters varies greatly from year to year. The letters from the beginning of the war (1914) are very pessimistic due to appeals to the poor organization of front-line life, heavy losses, and unsatisfactory training of personnel. At the beginning of 1915, the tone changed, which was probably due to an improvement in the combat situation, but at the end of the year the tone changed again to a pessimistic one, and decadent trends began to be traced, including the uselessness of this war. The letters of the Cossacks and those excerpts of which were published in newspapers are radically different; they are filled with patriotism, bravado and the expectation of an early victory. It is impossible not to note the influence of censorship: in some letters of 1914, the fighters directly point out the impossibility of writing about the real state of affairs at the front. © 2025 by Cherkas Global University.