Dataset provides information about pH in Lake Paione Inferiore (LPI) at different layer depths, at least twice (late summer/autumn) per year during the period 1978-2013. In total 354 records of pH in LPI for the period are uploaded. The ongoing studies of the water chemistry of Paione lakes aimed at monitoring their recovery from acidification or possible responses to climate warming (http://www.ise.cnr.it/research/global-change/altitude-lakes). The Paione lakes are an example of acid-sensitive environments which began in the 1990s to show signs of recovery, with an improvement in pH values and alkalinity and a decrease in sulphate concentrations in response to atmospheric loads.