The goal of this research was to identify large mammals that cause damage to sugarcane plantation and to determine the extent of the damage; this goal was achieved. The study on the damage caused by large mammals in Wonji-Shoa Sugarcane Plantation was carried out from August 2006 to March 2007. Three sample areas were randomly selected in the sugarcane plantation to collect data on sugarcane damage and faecal droppings of the animals. Strip line transect method was used to estimate hippopotamus population and total count method was used to estimate warthog and grivet monkey populations. Data collected on population estimation and faecal droppings were analysed using descriptive statistic chi-square and for damage assessment T-test was used. There was seasonal variation in the population of the three animals in the area. The estimated hippopotamus population was 129 and 99 during the wet and dry seasons, which was significantly different (χ 2 = 3.947, df =1, P < 0.05). The estimated warthog population was 180 and 140 during the wet and dry seasons, which was significantly different (χ 2 = 5.000, df = 1, P < 0.05). The estimated grivet monkey population was estimated 882 and 630 during the wet and dry seasons, which was significantly different (χ 2 = 42.00, df = 1, P < 0.01). More number of individuals were recorded during the wet season. The grivet monkey population was most abundant and the hippopotamus population was least abundant in the area. The sugarcane damage caused by hippopotamus was 2745 and 3089 stalk per ha during the wet and dry seasons which was significantly different (t = 16.96, df = 1, P < 0.05). Damage caused by warthog was 3988 and 4025 stalk per ha which was significantly different (t = 216.57, df = 1, P < 0.05). The sugarcane damage by grivet monkey was 3148 and 3590 stalk per ha during the wet and dry seasons which was significantly different (t = 15.244, df = 1, P < 0.05). Sugarcane damage increased during the dry season. Warthog caused more damage than hippopotamus and grivet monkey; hippopotamus caused least damage.