The study evaluated the effect of the carbon-chain spacer of monomers on the bonding effectiveness of two-step self-etching adhesive systems (SES). We investigated three acrylamidophosphonic acid monomers which vary only by the length of the carbon chain, 2-(N-methylmethacrylamido)ethylphosphonic acid, 6-(N-methylmethacrylamido)hexylphosphonic acid and 10-(N-methylmethacrylamido)decylphosphonic acid, on their effect in bonding performance while formulated in a self-etching primer with dentin and enamel. The results correlated well with those obtained from Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).It is concluded that there are no significant differences in terms of immediate Shear Bond Strength (SBS) on either enamel or dentin by using experimental self-etching primer (SEP) of different spacer chain length.