The objective of this study was to examine the effect of caffeine and sodium bicarbonate in a fertilization medium on the fertilizability of boar spermatozoa that were frozen in straws. Boar spermatozoa were extended with Beltsville F5 extender and frozen in 0.25-ml straws. In vitro matured porcine oocytes were fertilized in vitro (IVF) with frozen-thawed boar spermatozoa for 6h in a modified tris-buffered medium (mTBM) or in its modified medium by substituting the tris with 25mM sodium bicarbonate (modified bicarbonate-buffered medium; mBBM). Some of inseminated oocytes were fixed and stained for examination of sperm penetration. IVF embryos were cultured in a North Carolina State University-23 medium for embryo development. The percentage of live sperm was $47{pm}4%$ and morphological abnormality of acrosome was found in $14{pm}3%$ of spermatozoa. Optimal sperm concentration for IVF was $0.75{sim}1.0{ imes}1.0{ imes}10^6$ sperms/ml when mTBM containing 5mM caffeine was used as the fertilization medium. Sperm penetration was significantly (p<0.05) stimulated by increasing caffeine concentration in the IVF medium. In addition, mBBM significantly (p<0.05) increased sperm penetration (92%) compared to mTBM (65%). More (p<0.05) blastocysts (22% vs. 32%) developed from the oocytes that were fertilized in mBBM containing 1mM caffeine than from those fertilized in mTBM with 5mM caffeine. Our results indicate that boar spermatozoa can be frozen successfully in straws with holding their normal fertilizability and that caffeine and sodium bicarbonate stimulates sperm penetration in vitro.