The study presents results from analysis of funeral rite evolution at Celtic flat burial grounds in the territory of South-western, South-central and Eastern Slovakia (32 necropolises, 462 dated grave units). It selected burial grounds from the Lower Austria (Pottenbrunn), Transdanubia (Almasfuzito, Magyarszerdahely-Homoki dulo, Rezi-Rezicseri) and from the Tisa basin (Bodroghalom, Kiskotaj-Kultelkek, Muhi-Kocsmadomb) within the total of 220 graves. Statistical and comparative analyses were used for evaluation of the burial rite evolution and chronology of their expressions. Chronological frame of the work is representing by the Early and Middle La Tene period within the LTB1, LTB2 and LTC1 stages, with the absolute chronology ranging between the years 380-180 BC. The funeral rite development was analysed by five categories: 1 - graves representation by funeral rite and grave inventory character; 2 - grave pit shape and arrangement; 3 - treating with the deceased's grave inventory; 4 - way of arranging of cremated remains in grave; 5 - position of grave inventory toward cremated bones. Based on the analysis results, the funeral rite evolution was evaluated within four time intervals: 1 - early and middle phase of the LTB1 stage (cremation presented in the territory of the Lower Austria in the Early La Tene A stage and in Transdanubia); 2 - end of the LTB1 stage and the LTB1/B2 transitional horizon (occurrence of the first cremation burial in the territory of Slovakia - necropolis at Male Kosihy with the earliest cremation burials in the Slovak territory; cremation graves appear in Eastern Slovakia and the Tisa basin as well, where the Celts were contacted with the Vekerzug population, what is proved by cremation burials with mixed Celtic-Vekerzug inventory); 3 - the LTB2 stage up to the LTB2/C1 transitional horizon (transition to cremation and increasing number of cremation graves also at another burial grounds; shifting of occurrence of cremation burial westwards to the space between the lower Hron and Zitava river; partial abandoning the rigorous cremation rite at necropolises with cremation graves since this period); 4 - the LTC1 stage (cremation rite is present almost at each burial site; majority of grave inventories include undamaged artefacts; the strict cremation rite survives mainly in the south of Central Slovakia, in Eastern Slovakia and in the Tisa river basin; proportion of inhumation and cremation graves is almost even, what can be stated the true bi-rituality in the period under study).