Try this
SELECT *
FROM xxx
WHERE dates BETWEEN STR_TO_DATE('10/10/2012', '%m/%d/%Y')
AND STR_TO_DATE('10/12/2012', '%m/%d/%Y') ;
or
SELECT *
FROM xxx
WHERE STR_TO_DATE(dates , '%m/%d/%Y') BETWEEN STR_TO_DATE('10/10/2012', '%m/%d/%Y')
AND STR_TO_DATE('10/12/2012', '%m/%d/%Y') ;