We made detailed abundance analysis for ultimative test of membershipof twenty λ Bootis type stars candidates. Atmosphere parameters,LTE abundances for ten elements (including C and O) and NLTE values forNa were determined. We are able to confirm or establish the membershipfor nine objects (HD 23258, HD 36726, HD 40588, HD 74911, HD 84123, HD 91130,HD 106223, HD 111604 and HD 290799). Six stars (HD 90821, HD 98772, HD 103483, HD 108765, HD 201184 and HD 261904) can be definitely ruled out as beingmember of the λ Bootis group whereas no ambiguous decision canbe drawn for another five stars (HD 66684, HD 105058, HD 120500, HD 141851and HD 294253). We also tryed to find apparent spectroscopic binaries whichhave two solar abundant components mimic one metal-weak star as proposedby Faraggiana & Bonifacio (1999).