A surface mount device (S. M. D.) type miniature isolator has been developed. Its dimension is 6.8 6.9 4 mm3 and weight is 0.75 g. Both the volume and weight have been reduced to one-third compared with a conventional small model. A resin case and metalplated terminals on its surface are used to realize this configuration. By using a simplified simulation technique the most suitable ferrite size and the most suitable magnet are determined to minimize an insertion loss and to realize good temperature stability. Consequently, 0.8 dB insertion loss, 15 dB isolation and 14 dB return loss are obtained within 3 % bandwidth at 836.5 MHz in the practical operating temperature range between -25 and +75. Handling power capability of 2.5 W for forward input and 0.75 W for reverse input are achieved at +25.