Monster Island S.O.S (怪獣島SOS Kaijū-jima S.O.S) is the nineth episode of Return of Ultraman.
Intending to spend time with Aki and her little brother Jiro on his birthday, Go is assigned to fly to New York to pick up a new weapon created by the MAT branch there, a Monster Sonar Scanner. MAT member Minami disobeys orders and secretly takes Go's place. Flying back from New York, Minami encounters a typhoon, causing his MAT Arrow to crash on an island where he's rescued by some scientific researchers. The team of scientists explain they've been there investigating possible monster activity and this new sonar device will prove useful. A search of the island reveals a hibernating rock creature living within a cave. Minami suddenly falls ill so Go, feeling responsible, must get a serum to him in time before he expires from any one of three possible fates - tetanus, an unstable island, or a giant, rampaging monster.
- Hideki Go (郷 秀樹 Gō Hideki): Jiro Dan (団 時朗 Dan Jirō)
- Takeshi Minami (南猛 Minami Takeshi): Shunsuke Ikeda (池田 駿介 Ikeda Shunsuke)
- Ippei Ueno (上野一平 Uneo Ippei): Mitsui Hatashi
- Yuriko Oka (丘ユリ子 Oka Yuriko): Mika Katsuragi (桂木美加 Katauragi Mika)
- Katsushiro Kato (加藤勝一郎 ): Nobuo Tsukamoto (塚本信夫 Tsukamoto Nobuo)
- Fumio Kishida (岸田文夫 Kishida Fumo): Nishida Ken (西田健 Ken Nishida)
- Jiro Sakata (坂田 次郎 Sakata Jirō): Kawaguchi Hideki (川口英樹 Hideki Kawaguchi)
- Aki Sakata (坂田アキ Sakata Aki): Rumi Sakakibara (榊原るみ Sakakibara Rumi)
- Ken Sakata (坂田健 Sakata Ken): Shin Kishida (岸田 森 Kishida Shin)
- Return of Ultraman Vol.3 Episodes 9-12