The objective of the paper is to determine the allele frequencies for four X-chromosomal STRs determined in a population sample of 294 unrelated volunteers (191 males and 103 females) belonging to the Belarusian minority residing in northeastern Poland. A commercially available kit Mentype Argus X-UL (Biotype AG, Germany) was used to co-amplify X-STR loci: DXS8378, DXS7132, HPRTB and DXS7423. Electrophoresis and typing were performed by automated fluorescent detection in an ABI 310 Genetic Analyzer. The genotype distributions among the females conformed to HWE for all the analyzed loci. The evaluated quadruplex is a potential extension to a battery of autosomal systems in forensic applications, particularly in kinship analysis and in casework samples from sexual assaults.