Magnetic properties with three different sizes of Ni nanochains, synthesized by a techniqueof wet chemical solution, have been investigated experimentally. The sample sizes (averagediameter of the nano-particles) are 50, 75, and 150 nm, with a typical length of afew microns. The characterizations by XRD and TEM reveal that the samplesconsist of Ni nano-particles forming a one-dimensional (1D) chain-like structure.Magnetic properties have been investigated by temperature dependent magnetizationM(T) and field dependentmagnetization M(H) measurements. The results are explained within the context of the core–shell model. First, the freezingof disordered spins in the shell layer has resulted in a peak structure on the zero-field-cooled (ZFC)M(T) curve. The peak position is identified as the freezing temperatureTF. It is well described by the de Almeida–Thouless (AT) equation for thesurface spin glass state. Second, the shape anisotropy of the 1D structurehas caused a wide separation between the field-cooled (FC) and ZFCM(T) curves. This is mainly attributed to the blocking of the core magnetism by an anisotropy barrier,EA. Third,by the M(H) measurement in the low field region, the open hysteresis loop measured atT = 5 K<TF is significantly enlarged in comparison with that taken atT>TF. This indicates that a significant part of the contribution to the magnetic irreversibility atT<TF isarising from the disordered spins in the shell layer. Last, with the reduced sample size, the coercivity,HC, increases whereas the saturation magnetization goes down substantially. These implythat, as the sample size reduces, the effect of shape anisotropy becomes larger in themagnetization reversal process and the contribution to the magnetism from theferromagnetically ordered core becomes smaller.