Electrochemical response of synthetic oligonucleotides with different DNA bases sequences was investigated to find relationships between a chain composition and a signal. All DNA mononucleotides present electroactivity at a carbon paste electrode yielding anodic peaks at potentials: 1.00 (GMP), 1.28 (AMP), 1.47 (TMP) and 1.53 V (CMP). Also 15-mer homooligonucleotides show respective anodic peaks. Electrochemical response of 15- and 19-mer oligonucleotides consisting of all four DNA bases in different amounts was determined by the composition of oligonucleotide chain. When the contribution of different bases in oligonucleotide was balanced two anodic peaks were obtained that can be attributed to guanine and adenine moieties. Thymine residue is shown as a separate peak in voltammogram when its content in oligonucleotide chain is close to 50% of the total number of bases. Cytosine also yields a peak at its significant contribution in oligonucleotide chain and both pyrimidinic moieties produce catalytic waves easier when one of them is dominating or when only one pyrimidine derivative is present in a chain. Guanine is the easiest oxidized base and it produces a peak even at its minimal contribution (one guanine residue in 19-mer oligonucleotide). Guanine peak potential is dependent on oligonucleotide concentration and oligonucleotide composition. The lowest oligonucleotide concentration detected by guanine peak was 12.5 nM whereas detected by thymine peak was 90 nM.