This study was carried out to investigate the reproduction efficiency and disease of Holstein heifer grazed on mixed pasture desighed with association of tall fescue and white clover cultivar (3 treatments = TI : Tall fescue Fawn + White clover Regal + Orchardgrass + Perennial ryegrass, T2 : Tall fescue Roa + Ladino clover Regal + Orchardgrass + Perennial ryegrass, T3 : Tall fescue Roa + White clover Tahora + Orchardgrass + Perennial ryegrass) on reproduction efficiency and disease in Holstein heifers, ftom April 1994 to November 1996. The results are as follows: 1. Erythrocyte counts, hemoglobin and packed cell volume of hematological values were $8.12 imes10^6/{mu}ell, 9.9g/mell and 30.6mell/100mell$ respectively. While those were decreased to $4.84~5.93 imes10^6/{mu}ell, 7.0~7.8g/100mell and 22.8~28.3mell/100mell$, on pastuage (May-August), WBC counts was increased from $14.4 imes10^3/{mu}ell to 14.0~18.3 imes 10^{3/muell}$ on pasturage. No significant differences were detected among the treatments on pastures. 2. Parasitemia levels increased to $14.0pm8.2$(parasite/1,000rbc) at 1 month after pasturage. 3. At the occurrence of tirst estrus and conception, the average age of the Holstein heifers was $14.3pm1.9$ and $17.4pm1.5$ months, respectively, and the average interval of estrus cycle was $20.6pm1.0$ days. Howerer, there was no significant difference on reproductive efficiency among 3 treatments. 4. The outbreak of diseases were tick bane disease, pink eye, pneumonia, mastitis, gastroentitis, waterpoisoning ringworm papillon and atosis during pasturage period(may-october). These diseases were showed no significant difference among 3 treatments. 5. In conclusion, there are no significant difference on the reproductive effeciency and disease outbreak among three treatments.