Two studies were conducted to assess utilization of locally available feed ingredients for cattle fattening under traditional feedlotting system in North Western Tanzania. The first study involved identification of feed materials used for fattening in Misungwi and Kahama districts. Information on feed materials and diet formulation used by cattle fatteners were collected through focus group discussion. The feeds identified were analysed for chemical composition. In the second study, an on- station feeding experiment was conducted to assess the suitability of locally available feeds for cattle fattening. A total of 40 Tanzanian Shorthorn Zebu bulls with the age of three to four years and average weight of 172.6 ± 6.1 kg were used in the experiment. The animals were allocated to five dietary treatments (T 1 , T 2 , T 3 , T 4 and T 5 ) in a completely randomized design and the experiment took 70 days. Four animals were randomly assigned to each dietary treatment and each treatment was replicated twice. The ingredients of fattening diets were maize meal (MM), molasses (ML), maize bran (MB), rice polishing (RP), cotton seed hulls (CSH) and cotton seed cake (CSC). The compositions of the diets were as follows: T I (38% MM, 47% ML+ 0.5% urea), T 2 (45% MB, 37% CSH), T 3 (37% CSH, 45%RP), T 4 (30% CSH, 30% RP, and 22% MB) and T 5 -control (83.5% CSH + 1.5 local salts). Cotton seed cake (CSC) was used as a source of protein and comprised 13% of diet T 1 and 15% of T 2 , T 3 and T 4 diets. All diets were provided to the animals in adlib amount after grazing. Average feed intake (AFI), feed conversion ratio (FCR), average daily weight gain (ADG) and gross margin (GM) were determined. The results for focus group discussion show that CSH, CSC, MB and RP were the major feed ingredients used by local farmers for fattening. The majority (35.0%) of theiii respondents were using a diet composed of the mixture of CSH and CSC, but some were using either a mixture of CSH and RP (21.7%) or CSH alone (18.3%) to fatten cattle. In the feeding trial, AFI (5.58 kg DM/d) and FCR (10.27) were highest (P < 0.05) for the bulls fed T 5 . The highest ADG was observed on the bulls fed T 1 diet (0.90 kg/d) and differed (P ≤ 0.05) from that of animals fed T 3 (0.61 kg/d) and T 5 (0.58 kg/d), but not with the ADG of animals on T 2 (0.86 kg/d) and T 4 (0.83 kg/d) .The bulls fed T 1 had the highest (P < 0.05) cost per unit weight gain (3 337 TZS) and lowest GM (-58 661 TZS) whereas those on T 4 had the lowest (P ≤ 0.05) cost per unit weight gain (1 340 TZS) and highest GM (66 834 TZS). It is concluded that, the treatment diet T 4 is better than the other diets in traditional cattle fattening systems.