The 1991 Symposium on Nuclear data was held at Tokai Research Establishment, Japan Atomic Energy Research Institute (JAERI), on 28th and 29th of November 1991. This symposium was organized by Japanese Nuclear Data Committee and Nuclear Data Center, JAERI. In the oral session, presented were 15 papers on nuclear data activities in Thailand, status reviews of JENDL-3 and its special purpose files, OMEGA program and ESNIT promoted by JAERI and related nuclear data, reviews of nuclear theories, nuclear data in the intermediate energy region, topics on knowledge technology and reactor physics. In the poster session, twenty-three papers were presented, which were related to nuclear data measurements, benchmark tests of evaluated data and evaluation. All of the 38 papers are compiled in the proceedings.