The results of an experiment searching for quarks with charge from 2 3e to 1 3e, that are generated by 70 GeV protons on the Al target at zero angle, are reported. In the range of masses available at the IHEP accelerator quarks were not found. The upper limit estimation of the differential cross-section of quark production with mass {less-than or approximate} 5 GeV/c2 and the charge 2 3e equals to 7-9 × 10-36 cm2/ster GeV/c (90% confidence level). Total cross-section of quark production with charge 2 3e and mass 5-5 GeV/c2 does not exceed 4 × 10-37 cm2. © 1969.