Abstract: The study was conducted at Botswana College of Agriculture, Notwane-farm, Sebele, Gaborone for 150 days from June to October 2006. A flock of 60 Tswana sheep were used consisting of 30 males and 30 females. Fifteen of the males were castrates, 7 weaners and 8 lambs while the female group consisted of 15 ewes, 7 weaners and 8 lambs. Animals were weighed on monthly basis for five consecutive months, using Avery Walk-in Scale. The flock grazed daily for 8 h on a fenced natural pasture and were housed at night in kraals with corrugated roofing. Water was provided ad-libitum in kraals and feed supplements such as sorghum bran and salt lick were also provided. Lambs had access to lamb-finisher. The data collected were analyzed using the box-plot, between males and females. Linear multiple regression was used to analyze data within each age-group while Duncan�s multiple range test was used to separate the means. The means of male and females were different at p< 0.05. In month 1, means body weights (kg) were 32.4±17.5 and 27.2±14.0 for males and females, respectively. Final body weight (kg) after 150 days were 36.5±13.7 and 27.8±8.10 for males and females, respectively. Generally, all sheep age-groups showed a significant increase in growth although July which is the second month of the study drastic decline in growth rate was observed which is one of the coldest winter month in Botswana. It can be concluded from the study that growth rates of different age-groups of Tswana sheep under semi-intensive management are different and also there is interaction between time and gender and time and type/age-group. The time of the year is amajor factor that influenced the growth rate of range grazed Tswana sheep.