Lady Gaga, real name Stefani Germanotta, and her family said their final farewells following a small ceremony at St. Pius X Church in Montville.
The singer's on/off boyfriend Luc Carl was among the mourners.
The usually colourful Lady Gaga arrived at the church in a conservative black outfit.
Taking to her Twitter.com page the night before the ceremony, she paid tribute to her grandfather, writing, "Having a Perfect Manhattan, for my perfect guy. Love you Giuseppe."