the objective of this study was to evaluate the cryopreservation of in vitro mature or immature oocytes by conventional method. the experiment was conducted using oocytes of cows' ovaries from slaughterhouse, distributed into six treatments: unfrozen oocytes with the cumulus oophorus cells (t1) and naked (t2) which were submitted to the process of miv, fiv and civ; immature oocytes, with the cumulus oophorus cells (t3) and naked (t4), which were submitted to the cryopreservation, unfrozen and the miv, fiv and civ; oocytes with the cumulus oophorus cells (t5) and naked (t6), which were submitted to in vitro maturation, cryopreservation, and fiv and civ. the oocytes were frozen by the conventional methods, dehydrated by the immersion in three solutions with 0.6; 1.2 and 1.8 mol l-1 of ethylene glycol (eg) during 5 minutes each phase. the thawing phase was done by the immersion in water-bath at 30 oc during 20 seconds, and so, the oocytes were re-hydrated in three phases (0.9 mol l-1 eg + 0.3 mol l-1 of sacarose; 0.3 l-1 of sacarose without eg and sacarose) for six minutes each one. the mainly ultrastructural changes in cryopreserved matured oocytes were prematurely released of cortical granules. however, the frozen immature and mature oocytes showed vacuolization and disappearance of cristae mitochondrial. the frozen immature oocytes showed the maturation rate of 82.5, 75.4, 9.2 and 5.8% for t1, t2, t3 and t4, respectively. the fecundation rate were 56.2, 0.0, 38.7, 8.6, 63.6 and 16.7% and from the cleavage were 36.3, 7.9, 0.4, 0.0, 0.0 and 0.0% for t1, t2, t3, t4, t5 and t6, respectively. morula and blastocyst were observed only for unfrozen and naked oocytes (t1) (34.5%). these results showed that the frozen protocols affect the viability of the oocytes.