The presented research focuses on hand-built pottery produced in Latvia in the Middle and Late Iron Age (5th–12th centuries AD). The colour of vessel surface and the appearance of the sherd fracture surface are among the indicators of the conditions during fi ring. However, these primary features may have changed both in the course of the pottery use and after the respective vessel life ended and its sherds found their way into the occupation layer. Through experiments and with the help of X-ray powder diffraction analysis (XRPD) the authors seek to establish how the pottery fi ring process was organised, with special focus on determining the fi ring temperature interval. In the course of research 43 pottery samples from archaeological settlements and burial sites were analysed. Concurrently series of samples from several clay deposits of Latvia were taken. These samples were open-fi red imitating the hypothetical pottery fi ring regime. This was the fi rst time that XRPD analysis was used in the research of archaeological pottery of Latvia. The results of the analysis indicated that the samples had been fi red at a maximum temperature not lower than 600°C, but not higher than 900°C. The experiments allow the defi ning of the ancient pottery fi ring temperature maximum interval to fall within the range of 600–700°C.