The growing oocytes that are present in bovine ovaries in large numbers can be a potential resource for future livestock production. Here we describe a culture system that allows growing oocytes to survive for an extremely long period. Preantral follicles or oocyte-granulosa cell complexes in early antral follicles were isolated from bovine ovaries. The complexes/follicles were classified into three groups according to oocyte size, 90.0–99.5 μm (Class I), 80.0–89.5 μm (Class II), 70.0–79.5 μm (Class III), and were cultured for 20, 28 and 36 days, respectively. The rate of oocyte recovery decreased as the culture period increased. During the culture period, the mean oocyte size in Class I increased to about 115 μm. The mean diameters of Class II and III at the end of the culture periods were 107 μm and 102 μm, respectively. Since many oocytes, especially in Class II and III, still needed to grow to achieve full size, extension of the culture period and/or substantial improvement of the culture conditions are likely required.