Document and Entity Information	0 Months Ended
Sep. 27, 2013
Risk/Return:
Document Type	497
Document Period End Date	Sep. 27, 2013
Registrant Name	MFS SERIES TRUST I
Central Index Key	0000798244
Amendment Flag	false
Document Creation Date	Sep. 27, 2013
Document Effective Date	Sep. 27, 2013
Prospectus Date	Dec. 29, 2012
MFS® Research International Fund \| A
Risk/Return:
Trading Symbol	MRSAX
MFS® Research International Fund \| R4
Risk/Return:
Trading Symbol	MRSJX
MFS® Research International Fund \| 529A
Risk/Return:
Trading Symbol	EARSX
MFS® Research International Fund \| 529B
Risk/Return:
Trading Symbol	EBRIX
MFS® Research International Fund \| 529C
Risk/Return:
Trading Symbol	ECRIX
MFS® Research International Fund \| B
Risk/Return:
Trading Symbol	MRIBX
MFS® Research International Fund \| C
Risk/Return:
Trading Symbol	MRICX
MFS® Research International Fund \| I
Risk/Return:
Trading Symbol	MRSIX
MFS® Research International Fund \| R1
Risk/Return:
Trading Symbol	MRSGX
MFS® Research International Fund \| R2
Risk/Return:
Trading Symbol	MRSRX
MFS® Research International Fund \| R3
Risk/Return:
Trading Symbol	MRSHX
MFS® Research International Fund \| R5
Risk/Return:
Trading Symbol	MRSKX

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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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