Document and Entity Information	9 Months Ended
	Sep. 30, 2012	Nov. 01, 2012
Document and Entity Information
Entity Registrant Name	Astex Pharmaceuticals, Inc
Entity Central Index Key	0000919722
Document Type	10-Q
Document Period End Date	Sep. 30, 2012
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		93,495,334
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3