Isotachophoresis results indicate that the total concentrations of organic acids in Ordovician formation waters range from 9.17mg/L to 94.49mgPL and are obviously higher than those of Permo-Carboniferous formation waters. But both of them have the same compositional characteristics, i.e., acetic acid > > formic acid > propanoic acid > butanoic acid. The total alkyl phenol contents of Ordovician formation waters range from 0.57mg/L to 4.73mg/L, averaging 1.77mg/L. Among the samples for phenol detection, 47.06% samples contain less than 1.0mg/L, 35.29% samples 1.0-3.0mg/L, and only 17.65% samples more than 3.0mg/L alkyl phenol. The concentrations of organic acids and alkyl phenols in the Majiagou formation waters are of obviously heterogeneous distribution. There are several areas where the concentrations of organic acids and phenols are high in central Ordos Basin. These organic acid and phenol-high areas (organic acids >45mg/L and phenols > 2.0mg/L) are consistent with natural gas reservoir enriched areas in central Ordos Basin.