Magnetisation and a.c. susceptibility were measured for porous and high density polycrystalline La0.7Ca0.3MnO3 bulk samples synthesised by a conventional solid state reaction and a partial melting technique, respectively. A large irreversibility in the zero-field cooled and field-cooled magnetization was observed between 4.2 K and Curie temperature 270 K, for fields smaller than 200 Oe. Magnetization and a.c. susceptibility measurements gave a cusp at Tcusp. At Tcusp, a.c. susceptibility χ′ decreases with increasing frequency for the porous sample. The high density bulks having a sharp transition, but low Tc (250 K) exhibited a similar behaviour with a large irreversible magnetization at 50 Oe and a cusp in a.c. susceptibility for fields up to 1 Tesla. With increasing d.c. field, the irreversibility in magnetization was gradually suppressed. Large irreversibility in d.c. magnetization was explained by magnetic domain freezing instead of spin glass state. The small impurity particles embedded in large grains act as a stronger pining centre than weak-link grain boundaries for domains. © 1998 Elsevier Science Ltd. All rights reserved.