Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24-25 October 2008. The IW characteristics, viz. period (t sub (per)), velocity (C sub (vel)), wavelength (L), and wave numbers (k), are found to be 2.133-34.72 h, 0.135 km h sup (-1), 0.37-6.2 km and 2.70-0.16 cycles km sup (-1), respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E 0 = 3.34 J sup (-2)). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.