Selective alignment of nitrogen-vacancy (NV) centers in diamond is an important technique towards its applications. Quantification of the alignment ratio is necessary to design the optimized diamond samples. However, this is not a straightforward problem for dense ensemble of the NV centers. We estimate the alignment ratio of ensemble NV centers along the [111] direction in (111) diamond by optically detected magnetic resonance measurements. Diamond films deposited by N-2 doped chemical vapor deposition have NV center densities over 1 x 10 15 cm(-3) and alignment ratios over 75%. Although spin coherence time (T-2) is limited to a few ls by electron spins of nitrogen impurities, the combination of the selective alignment and the high density can be a possible way to optimize NV-containing diamond samples for the sensing applications. (C) 2015 AIP Publishing LLC.