<p class="Default">Progesterone (P) has been reported to affect several sperm functions especially capacitation and acrosome reaction<strong>. </strong>The main problem of (P) is its low aqueous solubility. So formulation of progesterone nanoparticles (PN) will enhance its solubility. This study was conducted to produce nanosized progesterone (NP) and assess its biocompatibility. Therefore, nine progesterone formulations were prepared and characterized. Data analysis revealed only one formula of P<span lang="EN-GB"> showed nanosized particle (1-100 nm) with an average particle size (</span><span>95±</span><span lang="EN-GB">5 nm), and spherical shape as seen by Transmission Electron Microscope(TEM).</span> Motile spermatozoa were separated from frozen-thawed semen by a swim-up procedure and capacitated in IVF-TALP medium with NP or P or without treatments (control) and incubated for 3h at 38°C and evaluated every 1 hour (h) interval. Ovarian oocytes were matured and fertilized <em>in vitro </em>with frozen-thawed bull sperm capacitated in vitro<strong> </strong>with NP or P or control (without NP, P) and incubated at 39C in 5% CO2 incubator for 24h and then examined for evidence of fertilization. In conclusion, this study demonstrates that nanosized progesterone is highly efficient for sperm capacitation. In addition to the use of nanosized progesterone in sperm capacitation produces more fertilized oocytes than the progesterone after<em> In Vitro </em>Fertilization (IVF).</p>