The King Seiko 56KS was a luxury watch produced by Suwa Seikosha for Seiko from 1968 to 1975.

Launching just as Seiko introduced their first-generation quartz watches in 1969, the 56KS series was more diverse and daring than its predecessors. It was an unusual product line, the only King Seiko produced by Suwa Seikosha rather than Daini Seikosha, who started the King Seiko line a decade earlier. As such, it fit somewhat awkwardly into the product line, overlapping somewhat with the slim and contemporary Suwa-produced King Seiko 52KS as well as the last of Suwa's handmade 36,000 Hi-Beat King Seiko 45KS line. Some models in the 56KS lineup strongly resembled the Grand Seiko line, especially Daini's legendary Grand Seiko 44GS, which had recently gone out of production.

Seiko produced many 56KS models at first, but it quickly became apparent that high-end watch buyers were more interested in the new quartz watches the company also produced. Sales and production fell dramatically as the 1970's got underway, with the line petering out in 1974 and 1975. But 1976 the King Seiko was no more, with the 56KS cancelled the previous year and the King Seiko 52KS being the last model in production.

Most of the 56KS lineup featured traditional “Grand Seiko Style” cases reminiscent of the Grand Seiko 44GS and it's descendants. This included the popular 562x-702x and 562x-704x models, which were available with day and date options. But there were some more radical members of the family, too The 5621-5010 was a pendant watch, the 562x-5010, 5050, and 5060 sported angular square cases, and the jewel-like 5626-5080 and 5626-6010 sported faceted cases and crystals. Some of these also featured colored dials in blue, green, orange, red, and purple.

The 56KS line shared Suwa's 5600 calibre, a mechanized and reliable movement bearing the “Hi-Beat” even though it only oscillated at 28,000 A/h rather than the 36,000 A/h seen in most King and Grand Seiko models of the previous half-decade. Thanks to mass production and automation, these movements have proven exceptionally accurate and reliable, with many still in use 40 years later. All King Seiko 56KS models have 25 jewel movements with a power reserve of 47 hours.

There were essentially three movement options in the King Seiko line

• 5621A/5621B (1969-1974) - Time only
• 5625A/5625B (1968-1975) - Date
• 5626A/5626B (1968-1974) - Day/date

These were produced in “A” (unregulated) and “B” (regulated) grades, with some being “Special” movements moving up to the next standard of accuracy. All “B” movements were chronometer grade, with many receiving official certification, as noted on the dial.

• King Seiko
• Seiko

• The History of Grand Seiko
• KS History