The effect of different diet of phytoplankton Cells on the growth performance of copepod, Oithonasp.in semi mass culture was examined in this research. This research used Chaetoceros calcitrans., Chlorella vulgaris., Nannochloropsis oculataand Isochrysis galbanaas diet to known the Oithonasp. growth performance. This research was designed by using Completely Randomized Design (CRD) with four treatments and three replicates. Those treatments were A.the culture was added with Chaetoceros calcitranscells diet, B.with Chlorella vulgaris.cells diet, C.with Nannochloropsis oculata. cells diet, and D.with Isochrysis galbana. cells diet, respectively. The results showed that the different diet of phytoplankton cells were highly significantly difference (P < 0,01) on Oithonasp. growth performance. The diet of Chaetoceros calcitranscell gave the best performance of Oithonasp. growth, where reached (6.963 ± 0.38) ind · mL–1of total density, (0.121 ± 0.003) ind · d–1of specific growth rate, and eggs production of (16.50 ± 2.74) eggs · ind–1.