This paper considers the magnetic properties of tidal flat sediments of the Yangtze Estuary and its relationship with particle size. The results indicate that magnetite of multi-domain (MD)/pseudo-single domain (PSD) in size dominates the magnetic properties of the samples. In addition to detrital magnetite, spherical magnetic particles are found in the magnetically strongest sediments near Shidongkou sewage outlet, which are ascribed to the product of industrial pollution. Particle size plays a strong role on the magnetic properties of the sediments. Magnetic susceptibility (c) and saturation isothermal remanent magnetization (SIRM) are positively correlated with the proportion of the fraction of 816 mm. However, magnetic parameters indicating fine-grained ferrimagnetic minerals, e.g. susceptibility of anhysteric remanent magnetization (cARM), are highly correlated with the fine fraction of <4 mm and even the fraction of <32 mm. The results indicate that, when c is used as a proxy for pollutant content, it is necessary to consider the possible influence of particle size on it. Due to the significant relationship between cARM and the fine component proportion, cARM can be applied to the normalization of pollutant content for particle size effect. This paper considers the magnetic properties of tidal flat sediments of the Yangtze Estuary and its relationship with particle size. The results indicate that magnetite of multi-domain (MD) / pseudo-single domain (PSD) in size dominates the magnetic properties of the samples . In addition to detrital magnetite, spherical magnetic particles are found in the magnetically strongest sediments near Shidongkou sewage outlet. Which are ascribed to the product of industrial pollution. Particle size plays a strong role on the magnetic properties of the sediments. Magnetic susceptibility (c ), and saturation isothermal with the proportion of the fraction of 816 mm. However, the magnetic parameters indicating fine-grained ferrimagnetic minerals, eg susceptibility of anhysteric remanent magnetization (cARM), are highly correlated with the fine fraction of <4 mm and even the fraction of <32 mm. The results indicate that, when c is used as a proxy for pollutant content, it is necessary to consider the possible influence of particle size on it. Due to the significant relationship between cARM and the fine component proportion, cARM can be applied to the normalization of pollutant content for particle size effect.