We studied the effect of three diets consisting of eggs and adults of two forms of Tetranychus urticae Koch (Acari: Tetranychidae) on the rate of predation, rate of oviposition, and development of the predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). The diet types consisted of T. urticae red form eggs/adults (type a), green form eggs/adults, (type b) and mixed red and green form eggs/adults (type c). The form of eggs did not have an effect on the rate of predation, nor did the forms of adults with the exception of more predation on mixed forms on the third day of the experiment and on both red and mixed forms on the second day. The rate of oviposition did not differ between N. californicus provided different forms of eggs as prey on the second day, but on the third day, there was a significantly higher rate of oviposition associated with diet types a, and c. There was no effect on rate of oviposition when N. californicus fed on adult prey. When T. urticaeeggs and adults were provided pairwise, N. californicus produced significantly more eggs when fed eggs of diet types a and c on both the second and third days of the experiment, while feeding on eggs and adults of the diet type b resulted in no difference in rate of oviposition. Moreover, preying on red T. urticae or on red and mixed T. urticae resulted in the slowest development of the protonymph and deutonymph stages, while the duration of larval stages were similar across all types of diets. The benefits of each diet and the capacity of N. californicusto control both forms of T. urticae are discussed.