King Hyŏnjong's period (r. 1664-1674) witnessed a real ingenuity in making astronomical instruments and clocks. While keeping traditional driving and time-annunciating mechanisms, innovative striking armillary clocks were made under the influence of the Western-style self-sounding clocks introduced via China and Japan. Song Iyŏng, Professor of Astronomy, made a demonstrational armillary clock using the Japanese self-sounding clockwork, and Yi Minch'ŏl, an Army Protector, made the armillary striking clepsydra using the traditional water-operated mechanism. In this paper Yi Minchŏl's four armillary clocks were investigated. The first made in 1664 was an improvement of Ch'oe Yuji's instrument of 1657. In 1669 Yi Minch'ŏl's second water-operated armillary clock of his own origin was created according to the petition by Song Chun'gil asking the restoration of the old Jade Clepsydra. It was repaired in 1687 by Yi Minch'ŏl himself and installed in the Chejŏng Pavilion (Chejŏnggak) during the reign of King Sukchong. The last repair was carried out in 1704 by An Chungt'ae and the fourth armillary sphere was located in the Kyujŏng Pavilion (Kyujŏnggak) during the reign of King Yŏngjo. The armillary sphere of the Chejŏng Pavilion is known to have been in operation even during the period of King Chŏngjo's reign, but Yi Minch'ŏl's armillary clocks had been missing afterwards. Examining the historical records and remaining Song Iyŏng's clock, the authors proposed a reconstructed model of Yi Minch'ŏl's water-operated armillary clock. It consists of three parts: an armillary sphere combined with the sun- and moon-carrying systems, a water-operated driving mechanism, and the time-annunciating mechanism. The armillary sphere and the striking mechanism are thought to have had very similar arrangement to those of the remaining weight-driven demonstrational armillary clock except for the differences in size and driving mechanism. The model was compared with King Sejong's two clepsydras — the Striking Clepsydra and the Jade Clepsydra — in terms of the driving and the time-annunciating mechanisms developed by Chang Yŏngsil who employed the Sino-Arabic technologies of the horological instruments. It was found that Yi's clocks were among the last survivors of the Korean tradition of the self-striking clepsydra since King Sejong and also of the East Asian water-operated time-keeping instruments.