Large improvement of room‐temperature ferromagnetism has been achieved in disk‐like self‐assembled Fe(1%)‐doped PbTiO3 nanocrystals synthesized by a hydrothermal reaction route, where KOH was used as precipitator, and poly(ethylene glycol) as a surfactant. Fe‐doped PbTiO3 nanocrystals assembled into disk‐like superstructure with a diameter about 10 μm. The saturation magnetization (Ms) of the Fe‐doped PbTiO3 sample is close to 7.54 × 10−2 emu/g with a coercive field (Hc) of 50 Oe, nearly 27 times larger than that reported previously (≈2.8 × 10−3 emu/g for Fe(1%)‐doped PbTiO3 using NH3·H2O as a precipitator). The improvement of ferromagnetism of the sample is attributed to the interface effect between the nanocrystals.