Note 10 - Business Segment Information - Segment Information (Details) - USD ($)		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue		$ 439,000	$ 364,000
Operating loss		(1,702,000)	(1,662,000)
Grant income		57,000	82,000
Interest expense		(757,000)	(985,000)
Depreciation		(16,000)	(16,000)
Research and development		(335,000)	(426,000)
Net loss		(2,616,000)	(2,749,000)
Loss on extinguishment		(214,000)	(184,000)
Tangible assets		1,565,000		$ 1,728,000
Investment in South Korean joint venture		99,000
Intangible assets		1,893,000		1,893,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture		99,000
Corporate, Non-Segment [Member]
Revenue
Operating loss		(972,000)	(948,000)
Grant income
Interest expense		(744,000)	(632,000)
Depreciation
Research and development		(202,000)	(172,000)
Net loss		(1,716,000)	(2,105,000)
Loss on extinguishment			(184,000)
Tangible assets		844,000		862,000
Intangible assets		1,893,000		1,893,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture		99,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue		298,000	301,000
Operating loss		(153,000)	(90,000)
Grant income
Interest expense
Depreciation		(5,000)	(4,000)
Research and development
Net loss		(153,000)	(90,000)
Loss on extinguishment
Tangible assets		423,000		410,000
Intangible assets
Operating Segments [Member] | Odor-No-More [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | Clyra Segment [Member]
Revenue
Operating loss		(306,000)	(287,000)
Grant income
Interest expense		(13,000)	(12,000)
Depreciation
Research and development		(14,000)	(49,000)
Net loss		(533,000)	(299,000)
Loss on extinguishment
Operating Segments [Member] | Clyra [Member]
Tangible assets		8,000		3,000
Intangible assets
Operating Segments [Member] | Clyra [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue		284,000	183,000
Operating loss		(43,000)	(110,000)
Grant income
Interest expense
Depreciation		(11,000)	(12,000)
Research and development		(82,000)	(122,000)
Net loss		(43,000)	(110,000)
Loss on extinguishment
Operating Segments [Member] | BLEST [Member]
Tangible assets		275,000		396,000
Intangible assets
Operating Segments [Member] | BLEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | BioLargo Water [Member]
Revenue
Operating loss		(228,000)	(227,000)
Grant income		57,000	82,000
Interest expense
Depreciation
Research and development		(180,000)	(209,000)
Net loss		(171,000)	(145,000)
Loss on extinguishment
Tangible assets		57,000		77,000
Intangible assets
Operating Segments [Member] | BioLargo Water [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Intersegment Eliminations [Member]
Revenue	[1]	(143,000)	(120,000)
Operating loss	[1]
Grant income	[1]
Interest expense	[1]
Depreciation	[1]
Net loss	[1]
Loss on extinguishment	[1]
Intersegment Eliminations [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue		(143,000)	(120,000)
Consolidation, Eliminations [Member]
Tangible assets	[1]	(42,000)		(31,000)
Intangible assets	[1]
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	[1]
Segment Reconciling Items [Member]
Revenue	[1]	143,000	120,000
Research and development	[1]	$ 143,000	$ 126,000

[1] the "elimination" column reflects an adjustment for revenues generated between our related entities and are eliminated in consolidation.