Magnetic penetration depth, λ m , was measured as a function of temperature and magnetic field in single crystals of low carrier density superconductor YPtBi by using a tunnel-diode oscillator technique. Measurements in zero DC magnetic field yield London penetration depth, λ L (T ), but in the applied field the signal includes the Campbell penetration depth, λ C (T ), which is the characteristic length of the attenuation of small excitation field, H AC , into the Abrikosov vortex lattice due to its elasticity. Whereas the magnetic field dependent λ C exhibit λ C ∼ B p with p = 1/2 in most of the conventional and unconventional superconductors, we found that p ≈ 0.23 1/2 in YPtBi due to rapid suppression of the pinning strength. From the measured λ C (T, H ), the critical current density is j c ≈ 40 A/cm 2 at 75 mK. This is orders of magnitude lower than that of conventional superconductors of comparable T c .