Excessive noise in nurseries has been found to cause adverse effects in infants, especially preterm infants in neonatal intensive care units (NICUs). The NICU design may influence the background sound level. We compared the sound level in two differently designed spaces in one NICU. We hypothesized that the sound level in an enclosed space would be quieter than in an open space. Methods: Sound levels were measured continuously 24 hours a day in two separate spaces at the same time, one enclosed and one open. Sound-level meters were placed near beds in each room. Sound levels were expressed as decibels, A-weighted (dBA) and presented as hourly Leq, Lmax, L10, and L90. Results: The hourly Leq in the open space (50.8-57.2 dB) was greater than that of the enclosed space (45.9-51.7 dB), with a difference of 0.4-10.4 dB, and a mean difference of 4.5 dB (p < 0.0001). The hourly L10, L90, and Lmax in the open space also exceeded that in the enclosed space (p < 0.0001). Conclusion: The sound level measured in the enclosed space was quieter than in the open space. The design of bed space should be taken into consideration when building a new NICU. Besides the design of NICU architecture, continuous monitoring of sound level in the NICU is important to maintain a quiet environment.