Organic - inorganic nanocomposites consisting of electroactive conjugated polymer, poly(3-hexylfhi-ophene) (P3HT), intimately tethered on the surface of semiconductor CdSe quantum dot (i.e., P3HT-CdSe nanocomposites) at the air/water interface formed via Langmuir isotherms were explored for the first time. The P3HT - CdSe nanocomposites displayed a high pressure plateau (~10.5 mN/m) in the Langmuir isotherm, illustrating their complex packing at the air/water interface. The packing of the Langmuir - Blodgett (LB) depositions of nanocomposites was revealed by AFM measurements. Furthermore, photovoltaic devices fabricated from the LB depositions of the P3HT - CdSe nanocomposites exhibited a relatively high short circuit current, I sc, while maintaining a thin film profile. These studies provide insights into the fundamental behaviors of semiconductor organic - inorganic nanocomposites confined at the air/water interface as well as in the active layer of an organic-based photovoltaic device.