Abstract: Phytoseiid mites Neoseiulus barkeri and N. cucumeris are the generalists mainly preying on spider mites and thrips, and widely used in agricultural biocontrol. In this paper, the cannibalism and intraguild predation of N. barkeri and N. cucumeris and the female aggressiveness on larvae (quantified as attack probability) in intraguild predation  were studied, aimed to elucidate the interrelationships between these two species of predatory mite to reasonably establish a combination of different natural enemies in biological control. The results showed that the phytoseiid mites consumed more con and heterospecific larvae, lesser protonymphs, and seldom con and heterospecific eggs. The adult females of the two species mites exhibited higher predation rates on heterospecific larvae and protonymphs than on conspecific larvae and protonymphs, suggesting that the two  species of mites preferentially engaged in intraguild predation in absence of other food sources. The predation rate of N. barkeri on heterospecific larvae and protonymphs was higher than that of N.  cucumeri. Moreover, N. barkeri was more aggressive to heterospecific larvae than N. cucumeri in intraguild predation. Therefore, N. barkeri was most probably a potential intraguild predator of N. cucumeris, whereas N. cucumeri was a potential intraguild prey when the intraguild predation occurred between N. barkeri and N. cucumeris.