The rocket landed near Khatzerim, a village just west of the southern desert city of Beersheva, a police spokeswoman said.
An army spokeswoman said it was the fourth incidence of firing since the truce came into effect at 0330 IST on Friday morning.
"The rocket hit an empty area without causing injuries or damage," a she said.
The latest ceasefire was put in place after a week of spiralling violence in and around Gaza which left 26 Palestinian and an Israeli dead.
An earlier truce announced last Sunday lasted less than 48 hours.
The fighting erupted after a deadly series of shooting attacks on a desert road just north of the Red Sea resort town of Eilat that killed eight Israelis and which Israel blamed on the Gaza-based Popular Resistance Committees.