This thesis looked at the concept of sonority and its influence in the acquisition of complex coda consonant clusters by ESL Spanish speakers. An experiment was performed to test the relationship between the sonority values of the segments of final complex clusters and the rate of errors. The goal of this thesis was to test the hypothesis that the Sonority Sequencing Principle was a powerful linguistic constraint that affected the acquisition of L2 phonology. The findings confirmed the idea that sonority played a crucial role in the phonological acquisition of L2 learners. Subjects reduced the least sonorant segment of the final cluster in order to achieve the minimal sonority descent. The choice of the segment could not be attributed to possible L1 interference since Spanish did not license complex codas and any final obstruents except /s/. The minimal sonority distance factor effected the rate of errors. Subjects produced more errors in clusters where the sonority distance between their segments was small (e.g., one, two, and three).