The paper deals with the analysis of Safety Factor in unsaturated pyroclastic slope instrumented at Monteforte Irpino in southern Italy. Suction and volumetric water content data from different depths over a five-year period and mechanical soil properties from laboratory tests have been used to estimate Safety Factor. First, a brief description of test site with geotechnical soil properties is reported and in situ data monitoring used for the estimation of Safety Factor are introduced. Then, in order to analyse the effect of the seasonal trend of pore pressure on the Safety factor of the slope, a limit equilibrium analysis is performed by modelling the slope at the test site as an infinite one. In the analysis Bishop’s effective stress approach is used. In particular the Safety Factor over five years is plotted and the effects of matrix suction on the slope stability is examined. Profiles of Safety Factor at fixed days during wet period are also shown to locate the critical sliding surface. Moreover parametric analyses were carried out, in particular the suction values on the sliding surface assumed at 2.00 meters from the ground surface were calculated varying the slope angle of the monitored infinite slope keeping constant the value of Safety Factor.