  We present the photometric and spectroscopic evolution of the type IIn SN
1995G in NGC 1643, on the basis of 4 years of optical and infrared
observations. This supernova shows very flat optical light curves similar to SN
1988Z, with a slow decline rate at all times. The spectra are characterized by
strong Balmer lines with multiple components in emission and with a P-Cygni
absorption component blueshifted by only 700 km/s. This feature indicates the
presence of a slowly expanding shell above the SN ejecta as in the case of SNe
1994aj and 1996L. As in other SNe IIn the slow luminosity decline cannot be
explained only with a radioactive energy input and an additional source of
energy is required, most likely that produced by the interaction between
supernova ejecta and a pre--existent circumstellar medium. It was estimated
that the shell material has a density n(H) >> 10^8 cm^-3, consistent with the
absence of forbidden lines in the spectra. About 2 years after the burst the
low velocity shell is largely overtaken by the SN ejecta and the luminosity
drops at a faster rate.
