Reconstructing the palaeodiet of populations associated with the Lusatian Urnfields is an important part of the study of prehistoric communities. It is particularly important because of the limitations arising from the widespread use of cremation in this period, which precludes the determination of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in bone collagen. The stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were analysed in bone samples selected from the 23 individuals recovered from inhumation burials in the bi-ritual cemetery of the Lusatian Urnfields in Świbie, Gliwice District. Samples from preserved fragments of long bone shafts and cranial bones, and in one case a fragment of the last lumbar vertebra, were selected for analysis. Due to the very poor state of preservation of the skeletons, it was impossible to carry out palaeodiet reconstruction studies for many of the individuals. No animal bones with diagnostic characteristics were preserved in the Świbie cemetery, so the trophic background was determined based on the published data for fauna from Neolithic and Late Bronze Age sites. All bone samples were mechanically cleaned. The obtained samples were then subjected to the standard collagen extraction procedure used in the Radiocarbon and Mass Spectrometry Laboratory, which is based on the modified Longin method. For most of the individuals examined, some measurements of stable carbon and nitrogen isotopes were obtained despite their clear, macroscopically determined contamination with organic compounds. Most of the samples analysed showed a C/N ratio that met the quality criterion, which ranged between 2.9 and 3.6. Samples of two individuals, from graves 2 and 259, were contaminated, with subsamples for the individual from grave 2 well outside the range obtained for the others. The δ13C values ranged from -21.22‰ to -17.63‰ (X = -18.86; S.D. = 0.825), while the δ15N values ranged from 4.62‰ to 9.5‰ (X = 8.25; S.D. = 1.003), excluding the data for the contaminated samples. The sample selected for an adult of undetermined sex, from grave 2, came from a pre-WWII excavation carried out around 1936. The contamination, shown by isotopic testing, most likely came from a preservative, which was probably isinglass (fish glue). It was most likely made from the swim bladders of freshwater fish. Most of the individuals examined to establish their palaeodiet were characterised by a high trophic level, indicating a balanced diet based on food of inland origin, with C3 plants and a high proportion of food of animal origin. The individual of undetermined sex and age at death from grave 79 was characterised by a plant-based diet. Individuals falling into the Infans I, Infans II and child age categories, due to their likely high milk consumption, were characterised by the highest δ15N parameters, which are characteristic of a ‘pastoral diet’. The range of stable carbon (δ13C) and nitrogen (δ15N) isotope values obtained for the male individuals placed them at a slightly higher trophic level than the females, but these differences were not statistically significant (Mann-Whitney U test: for δ13C p-value 0.88076; for δ15N p-value 0.64552). Individuals of indeterminate sex and age at death displayed a wide range of carbon and nitrogen isotope values.