The effects of anthropogenic sound on marine mammal behavior are typically estimated based on sound pressure level (SPL) and do not consider the possible effects of sound duration. In some cases, the perceived loudness of sound may be a better metric than SPL in predicting behavioral reactions of marine mammals to sounds of varying duration. As a perceptual attribute of sound, loudness cannot be directly measured. Perceived loudness is often measured using a comparison task, which makes it difficult to test in nonhuman animals. In this study, the training and methodology were uniquely designed to directly measure how perceived loudness changes as a function of sound duration in bottlenose dolphins. Two bottlenose dolphins were trained to perform a two-alternative forced choice (2AFC), loudness comparison task, where they listened to two 40 kHz tones at different SPLs and various durations and chose the louder sound via a paddle press. Preliminary data collection focused on two signals with equal duration but different SPLs, to determine baseline variability. This chapter discusses the training and methodology, the preliminary results, and how they compare to a previous study that tested amplitude discrimination thresholds for a 40 kHz, 5 ms signal.