The mo rpholo gy of co rt ical react io ns dur ing o ocytes act ivat ion in shr imp Penaeus chinensi s is de scr ibed in this pape r. In the peripheral o oplasm there a re many co rt-i cal specializat ions-r ods, w hich ar e perpendicular to the oo lemma and located in the co rt ical cr ypt fo rmed by the subsided v itelline enve lope. The co rt ical of the P. chinensis does not need the exist ing of the sperm. When an o ocyte is spawned into se a water, it start s the cort ical react ion. The co rt ical ro ds ar e expelled and f orm a cor ona ar ound the egg. This co rona remains as the ro ds swell and begin to dissipate f r om the end o f the ro ds. With the rods dissipat ing completely, the cor ona disappears. The o ocytes accomplish the meiosis and r elea se the f ir st and seco nd po lar bo dies. A hatching membr ane also forms and ends the cort ical react ion. The funct ions of the cort ical react ion a re a lso discussed.