The rocket landed in an open area south of Ashkelon. There were no reports of injuries or damage.
Two hours later, another rocket landed in the Shaar Hanegev Regional Council. There were no injuries in this incident as well.
More than 100 Qassam rockets have been fired at Israel since the ceasefire with the Palestinians came into force about a month and a half ago.
On Monday, Palestinians fired a Qassam rocket at Israel in the afternoon hours. The rocket landed in an open area near the southern town of Sderot. There were no reports of injuries.
'An imaginary calm'
The issue of Qassams fired at Ashkelon, Sderot and western Negev communities was raised during Sunday's cabinet meeting. Minister Avigdor Lieberman demanded a wide-scale Israel Defense Forces operation, after which Europe would have to send in 30,000 NATO soldiers to maintain the operation's accomplishments.
Deputy Prime Minister Eliyahu Yishai said: "They ask us to wait and wait and wait and in the end we will pray a price for that. The implications are a return to what was in Lebanon, where we waited for years and gave Hizbullah time.
"The same will happen here too, they will continue to dig tunnels, to smuggle weapons and organize. There is no ceasefire and we are turning a blind eye."
"We chose an imaginary calm when we claimed that a response is likely to escalate the situation. This is not right. I believe that in the end we will act and a decision will be taken soon. We need shouldn't act hastily but in an organized and planned manner that will reduce their options considerably," he said.