Effects of season and sex on voluntary dry matter intake (DMI), growth, digestibility and performance of the Fiji Fantastic sheep fed native guinea grass (Panicum maximum) was investigated. Twelve lambs (6 ram lambs and 6 ewe lambs) from the sheep-breeding unit, Nawaicoba (Fiji) were selected and used in the two seasonal phase trials. Six lambs each (3 ram and 3 ewe), with pre-trial liveweight and age 25.1±1.15 kg and 5-6 months, and 20.0±0.00 kg and 4-5 months of age were used in dry and wet seasons (trials 1 and 2), respectively. The lambs in each trial were selected as closely as possible for liveweight. The experimental design was a completely randomized 2 × 2 factorial [(2 seasons (dry and wet) × 2 sexes (females and males)]. Trial 1 was from October 3^rd 2002 - 28^th January 2003 (92 days), while trial 2 was from February 12^th - 8^th May 2003 (84 days). Seasons had effects on chemical composition of the forage. Except for crude protein (CP), dry matter (DM), neutral detergent fibre (NDF), acid detergent fibre (ADF), hemicellulose, cellulose and energy (MJ/kg, DM), were higher in the dry (D) than in the wet season (W). DMI of sheep was 536±0.50 and 792±7.51g/head/d in D and W seasons, respectively. Season but not sex had significant (P<0.001) effect on DMI. ADG was 34.5±2.5 and 35.5±3.5 g/head/d and season and sex had no significant (P>0.001) effects on ADG. Feed efficiency (kg DMI/kg liveweight gain) was 15.6±1.1 and 22.5±2.0 in D and W seasons, respectively. Water intake (WI) in D and W seasons was 1328.8±9.9 and 550.2±9.8 L, respectively. Season and DMI had significant (P<0.001) effect on WI. Blood urea-N and blood glucose concentrations at the pre-and post-experimental periods were similar and sex had no effect on their concentrations. Season but not sex had effect on apparent digestibility of CP, NDF, hemicellulose and energy. Also, season had significant effect (P<0.001) on nutritive value index (NVI) of guinea grass. Daily CP intake (DCPI) was 3.6±0.10 and 9.4±0.05 g/kgW^0.75/d in D and W seasons, respectively. Our data confirmed that native guinea grass in the unit would not adequately support the growth of lambs in the D and W seasons because of its poor nutritive quality. In conclusion, supplementation is recommended to improve liveweight gain and general performance of the Fiji Fantastic sheep on sole diet of native guinea grass in the D and W seasons.