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Note 1 - Nature of the Business and Basis of Preparation - Schedule of Subsidiaries (Details)	Sep. 30, 2021
BeyondSpring Pharmaceuticals Inc. [Member]
Equity method investment, ownership percentage	100.00%
BeyondSpring Ltd. [Member]
Equity method investment, ownership percentage	100.00%
BeyondSpring HK Limited [Member]
Equity method investment, ownership percentage	100.00%
Wanchun Biotechnology Limited [Member]
Equity method investment, ownership percentage	100.00%
Wanchun Biotechnology (Shenzhen) Ltd. [Member]
Equity method investment, ownership percentage	100.00%
Dalian Wanchunbulin Pharmaceuticals Ltd. (“Wanchunbulin”) [Member]
Equity method investment, ownership percentage	58.00%
BeyondSpring Pharmaceuticals Australia PTY Ltd. (“BeyondSpring Australia”) [Member]
Equity method investment, ownership percentage	100.00%
Beijing Wanchun Pharmaceutical Technology Ltd. [Member]
Equity method investment, ownership percentage	58.00%
SEED Therapeutics1 Inc. [Member]
Equity method investment, ownership percentage	59.00%
SEED Technology Limited [Member]
Equity method investment, ownership percentage	58.00%
SEED Therapeutics US, Inc. [Member]
Equity method investment, ownership percentage	59.00%

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- Definition

Represents the percentage of ownership in subsidiaries.

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No definition available.

+ Details

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- Details

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- Details

Name:	srt_OwnershipAxis=bysi_BeyondSpringLtdMember
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Name:	srt_OwnershipAxis=bysi_BeyondspringHkLimitedMember
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Name:	srt_OwnershipAxis=bysi_WanchunBiotechnologyLimitedMember
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- Details

Name:	srt_OwnershipAxis=bysi_WanchunBiotechnologyShenzhenLtdMember
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X

- Details

Name:	srt_OwnershipAxis=bysi_DalianWanchunbulinPharmaceuticalsLtdWanchunbulinMember
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- Details

Name:	srt_OwnershipAxis=bysi_BeyondspringPharmaceuticalsAustraliaPtyLtdBeyondspringAustraliaMember
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X

- Details

Name:	srt_OwnershipAxis=bysi_BeijingWanchunPharmaceuticalTechnologyLtdMember
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Data Type:	na
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Name:	srt_OwnershipAxis=bysi_SEEDTherapeutics1IncMember
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Data Type:	na
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Name:	srt_OwnershipAxis=bysi_SEEDTechnologyLimitedMember
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Data Type:	na
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X

- Details

Name:	srt_OwnershipAxis=bysi_SeedTherapeuticsUSIncMember
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