The relationships between body weight, clutch size, length of breeding season, breeding frequency, incubation and nestling periods were studied in the Australian passerines. The means of the above factors as well as allometric equations were calculated for all Australian passerines and separately for the four major families (Maluridae, Meliphagidae, Muscicapidae and Ploceidae) and six zones of distribution (all Australia; Bassian; Torresian; Torresian and Bassian; Irian; Eyrean). The mean clutch size of Australian passerines is significantly smaller than that of North African passerines. This is because the old invaders to Australia (e.g. the Meliphagidae, Maluridae and Muscicapidae) have significantly smaller clutches than the new invaders (e.g. Ploceidae and Corvidae). A significant difference in clutch size was found between the Irian and Eyrean zones, supporting an early claim by Kikkawa. Negative correlations were found between body weight and clutch size, length of breeding season and breeding frequency. These indicate that small passerines in Australia tend to have larger clutches and longer breeding seasons and to breed more frequently than larger species. Body weight is positively correlated with both incubation and nestling period, as found for other altricial birds. There are no significant differences in incubation length between the zones, but there are differences among the families. The ecological implications and the possible reasons for the above correlations and differences between the groups are discussed.