The aim of the present study was to determine changes in body weight gain and the level of selected biochemical blood serum parameters under conditions of diminished calcium content in rat diet and after introducing inulin-type fructans into the diet. The effect of inulin or oligofructose on the content of calcium in femur was studied as well. The 21-day experiments were carried out on albinotic male Wistar rats. The animals were fed with semi-synthetic AIN’93 G diet with various amounts of calcium in a mineral mix (Ca₁₀₀, Ca₅₀, Ca₂₅) and containing inulin (Ca₅₀+I, Ca₂₅+I) or oligofructose (Ca₅₀+OF, Ca₂₅+OF) in conditions of Ca deficiency – 50% and 75%, respectively. Our results showed that the level of total and ionised calcium, magnesium and phosphorus in blood serum as well as Ca content in femur varied with the amount of Ca in rat diet. The intake of inulin-type fructans increased significantly Ca content in rat femur, both at 50% (33% w/w Ca in the Ca₅₀ group vs. 38% w/w for animals fed diet with inulin, and 37% w/w for oligofructose fed rats) and 25% of the recommended dietary calcium level (25% w/w Ca₂₅ group, 31% - after inulin intake, and 30% after oligofructose consumption).