In September 1991 we started a photoelectric monitoring of O VI PNNi that are candidate to be non radial pulsators. The observations were obtained using the two head photometer described by Piccioni et al. (1979, Acta Astron. 29,463), mounted on the 1.5 m telescope of the Bologna Observatory. We generally used the B and sometimes the U filter; only BA 1 was always observed without filters because of its faintness. The reductions have been pursued by means of a program that yields the moving averages of the counts of the variable and comparison star. For the search of periodicities the methods of Deeming (Kurtz 1985, MNRAS 213,773) and Scargle (1982, Ap J 263,835) were principally used. The list of observations is reported in the following Table, where σ is the mean value of the standard deviations obtained by computing the moving averages.