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Document and Entity Information	9 Months Ended
	Sep. 30, 2016
Document Information [Line Items]
Document Type	S-4/A
Amendment Flag	true
AmendmentDescription	Amendment No. 1
Document Period End Date	Sep. 30, 2016
Trading Symbol	MBCN
Entity Registrant Name	MIDDLEFIELD BANC CORP
Entity Central Index Key	0000836147
Entity Filer Category	Smaller Reporting Company

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The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word "Other".

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A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

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