The present study investigated the extent to which native English listeners' perception of Japanese length contrasts can be modified with perceptual training, and how their performance is affected by factors that influence segment duration, which is a primary correlate of Japanese length contrasts. Listeners were trained in a minimal-pair identification paradigm with feedback, using isolated words contrasting in vowel length, produced at a normal speaking rate. Experiment 1 tested listeners using stimuli varying in speaking rate, presentation context (in isolation versus embedded in carrier sentences), and type of length contrast. Experiment 2 examined whether performance varied by the position of the contrast within the word, and by whether the test talkers were professionally trained or not. Results did not show that trained listeners improved overall performance to a greater extent than untrained control participants. Training improved perception of trained contrast types, generalized to nonprofessional talkers' productions, and improved performance in difficult within-word positions. However, training did not enable listeners to cope with speaking rate variation, and did not generalize to untrained contrast types. These results suggest that perceptual training improves non-native listeners' perception of Japanese length contrasts only to a limited extent.