Penelitian ini bertujuan untuk mengetahui faktor-faktor yang mempengaruhi overoptimisme investor pada awal perdagangan di pasar sekunder dan menguji penganth optimisme investor dan kinerja pemsahaan pra-IPO terhadap long-run underpeiformance saham pasca IPO. Faktor-fakor yang di duga berpengaruh terhadap ovcroptimisme investor dan long-run underpeiformance adala.h debt to equity ratio (DER), operating pro/it margin (OPM), dan fora! asset turn over (T ATO) pada dua ta.hun dan satu tahun scbclum IPO ser-ta kinerja opcrasi IPO secara rata-rata yang terdapat dalam prospektus penisahaan. Fakror DER, OPM, dan TATO tidak terbukti secara konsisten berpengaruh terhadap overoptimisme investor pada awal perdagangan. Variabel DER sat1.| tahun dan DER rata-rata dua tahun sebelum IPO terbukti secara konsisten berpengaruh positif signifikan terhadap underperformance saham IPO pada I2 bulan Setelah IPO. Sedangkan overoptimisme investor terbukti berpengaruh negatif signifikan terhadap buy-and-hold return I2 buian pasca IPO

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This research has purpose to explore several factors that influence investor over-optimism in early trade in secondary market and to test the influence of investor over-optimism and pre-IPO company perfomance to stocks?s long-run underperformance after IPO. Several factors that estimated have influence to investor over-optimism and pre-IPO company performance is debt to equity ratio (DER), operating profit margin (OPM), and total asset tum over (TATO) in two years and one year before IPO, and average IPO operational performance which is contained in company prospectus. The results show that DER, OPM, and TATO not proved consistently have influence to investor over-optimism in early trade. One year DER and two years average DER before IPO proved consistently have significant positive influence to IPO stocks underperformance in I2 months aher IPO. Investor over-optimism proved has significant negative intluenee to I2 months buy-and-hold retum post IPO.