Boiling heat transfer characteristics of freon R-113 are experimentally investigated in a vertical small diameter tube, D = 1.45 mm and L = 100 mm at a wide pressure range of 19-269 kPa under natural circulation condition. Except the entrance region of the test section, the flow regime is annular in view of the measured vapor flux. The pool boiling correlations of Stephan and Abdelsalam, and McNelly equally well predict the experimental data within an error of +/-20%. No enhancement of heat transfer coefficient is obtained although D/B is less than 1.5, which differs from the finding of Klimenko.