Laccases are multicopper enzymes that catalyze oxidation of electron-rich substrates coupled to reduction of molecular oxygen to water. Since the Type 1 copper (T1 Cu) is the site where electrons are withdrawn from the substrate, it is assumed that the reduction potential of this copper correlates with enzyme activity. Herein, we studied the correlation of the T1 Cu reduction potential and the enzymatic activity of the small two-domain laccase Ssl1 from Streptomyces sviceus. For a systematic approach, we aimed to minimize any effects other than the reduction potential difference. To this end, we constructed a series of Ssl1 mutants with reduction potentials varying from <290 to 560 mV. Along with the hydrophobicity of the axial ligand of the T1 Cu also structural changes in the substrate binding site and additional hydrogen bonding increased the reduction potential. Enzyme activity experiments demonstrated that the T1 Cu reduction potential has a different effect on oxidation of different substrates. Whereas there was no obvious correlation between the T1 Cu reduction potential and kinetic parameters for the oxidation of syringaldazine (with a reduction potential of 390 mV), a good correlation was observed between the T1 Cu reduction potential and the conversion of substituted phenols with reduction potentials between 660 and 820 mV. This correlation was pronounced for the Ssl1 variants with reduction potentials above 470 mV, which demonstrated increased activities also during the oxidation of two dyes, alizarin red S and indigo carmine. How the environment of the Type 1 copper of a laccase influences the enzyme activity remains an intriguing question. In this work, we constructed mutants of a small laccase from Streptomyces sviceus with reduction potentials ranging from <290 to 560 mV, and evaluated their activity towards high- and low-potential substrates. Display omitted •Mutants of Ssl1 laccase with reduction potentials between <290 and 560 mV were constructed.•Reduction potential of the Type 1 copper (T1 Cu) correlated with the axial ligand hydrophobicity.•Activity towards substituted phenols correlated with the T1 Cu reduction potential.•Ssl1 variant with a reduction potential of 560 mV oxidized substrates not accepted by wild type.