Note 7 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	Aug. 31, 2022	Aug. 31, 2021
Current assets	$ 40,234,881	$ 33,747,089
Total assets	86,193,953	74,370,879
Current liabilities	17,065,401	8,516,196
Noncurrent liabilities	1,884,256	104,102
Joint ventures’ equity	63,595,262	62,368,026
Investments in joint ventures	21,814,754	27,623,768
EXCOR and All Other Joint Venturs [Member]
Investments in joint ventures	21,814,754	27,623,768
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	21,256,923	24,702,778
EXCOR [Member]
Investments in joint ventures	12,494,320	15,412,574
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	12,463,415	14,697,490
All Other [Member]
Investments in joint ventures	9,320,434	12,211,194	[1]
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	8,793,508	10,005,288	[1]
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Current assets	52,428,831	69,394,796
Total assets	55,854,457	73,814,402
Current liabilities	10,981,833	16,366,398
Noncurrent liabilities	1,138,980	1,455,524
Joint ventures’ equity	43,733,644	55,992,480
EXCOR [Member]
Current assets	26,047,914	33,886,655
Total assets	27,932,532	36,211,520
Current liabilities	2,943,895	5,386,377
Noncurrent liabilities	0	0
Joint ventures’ equity	24,988,637	30,825,144
All Other [Member]
Current assets	26,380,917	35,508,141	[1]
Total assets	27,921,925	37,602,882	[1]
Current liabilities	8,037,938	10,980,021	[1]
Noncurrent liabilities	1,138,980	1,455,524	[1]
Joint ventures’ equity	$ 18,745,007	$ 25,167,336	[1]

[1] Includes Zerust India since Zerust India was not a consolidated subsidiary of the Company as of August 31, 2021 or May 31, 2021. See Note 3 entitled “Business Combination.”