Note 6 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	Feb. 28, 2023	Aug. 31, 2022
Current assets	$ 39,602,851	$ 40,234,881
Total assets	86,136,754	86,193,953
Current liabilities	16,078,289	17,065,401
Noncurrent liabilities	1,824,222	1,884,256
Stockholders’ equity	64,790,600	63,595,262
Investments in joint ventures	21,522,496	21,814,754
EXCOR and All Other Joint Venturs [Member]
Investments in joint ventures	21,522,496	21,814,754
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	20,493,861	21,256,923
EXCOR [Member]
Investments in joint ventures	12,106,429	12,494,320
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	12,075,524	12,463,415
All Other [Member]
Investments in joint ventures	9,416,067	9,320,434
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	8,418,337	8,793,508
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Current assets	54,425,899	52,428,831
Total assets	57,924,227	55,854,457
Current liabilities	14,002,680	10,981,833
Noncurrent liabilities	346,645	1,138,980
Stockholders’ equity	43,574,902	43,733,644
EXCOR [Member]
Current assets	25,538,114	26,047,914
Total assets	27,376,219	27,932,532
Current liabilities	3,163,365	2,943,895
Noncurrent liabilities		0
Stockholders’ equity	24,212,854	24,988,637
Joint Ventures in France [Member]
Current assets		26,380,917
Total assets		27,921,925
Current liabilities		8,037,938
Noncurrent liabilities		1,138,980
Stockholders’ equity		$ 18,745,007
All Other [Member]
Current assets	28,887,785
Total assets	30,548,008
Current liabilities	10,839,315
Noncurrent liabilities	346,645
Stockholders’ equity	$ 19,362,048