The other Osmond brothers helped produce the Donny and Marie show
Donny and Marie Osmond's Las Vegas greatest hits show is being extended until October 2010, organisers say.
The decision was taken because of the popularity of their 90-minute spectacle, which opened last month.
The siblings were booked for the Flamingo Showroom to replace singer Toni Braxton, who ended her show in April due to ill health.
The musical pair hosted their own popular programme on US television during the 1970s.
"Donny and Marie are timeless entertainers and cultural icons," Flamingo president Don Marrandino said when their residency was announced earlier this year.
The pair were originally booked to perform from Tuesday through to Saturday for 26 weeks spread out over eight months.
The Osmonds - made up of five brothers with Donny as lead singer - were one of the biggest pop acts of the 1970s.
From 1976 to 1979 Donny and sister Marie Osmond branched out to host the TV programme the Donny and Marie show, which their older brothers helped produce.
The pair also hosted a talk show in the US with the same title from 1998 to 2000.
Marie Osmond was a recent contestant on Dancing With The Stars.