Note 1 - Business and Organization (Details Textual)		3 Months Ended						6 Months Ended	9 Months Ended
	Mar. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2017
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total		$ (2,390,000)	$ (2,700,000)	$ (2,616,000)	$ (3,886,000)	$ (1,987,000)	$ (2,749,000)		$ (7,707,000)	$ (8,625,000)
Net Cash Provided by (Used in) Operating Activities, Total									(3,318,000)	(3,181,000)
Working Capital		(1,316,000)						$ (1,316,000)	(1,316,000)
Assets, Current, Total		$ 1,873,000						$ 1,873,000	1,873,000		$ 1,065,000
Proceeds from Issuance of Common Stock									$ 2,380,000
Number of Wholly-Owned Subsidiaries		4						4	4
BioLargo Engineering, Science & Technologies, LLC [Member]
Noncontrolling Interest, Ownership Percentage by Parent		97.50%						97.50%	97.50%			100.00%
BioLargo Engineering, Science & Technologies, LLC [Member] | Clyra Medical Technology Inc [Member]
Noncontrolling Interest, Ownership Percentage by Parent		47.00%						47.00%	47.00%
Lincoln Park Capital Fund, LLC [Member]
Proceeds from Issuance of Common Stock	$ 250,000	$ 797,000		$ 295,000				$ 1,043,000	$ 1,700,000
Average Proceeds per Month from Issuance of Common Stock									$ 160,000