Abstract: A field experiment to determine the influence of root rot on dry matter partition of three cassava cultivars planted in the Sabongidda-Ora humid forests and in the Ibadan derived savanna of Nigeria was carried out from July 2003-November 2005. In each location, healthy cassava stems of three varieties; TME-1 (local), TMS 30572 and TMS 4 (2) 1425 (both improved) were planted in a randomized complete block design with 3 replications. Dry matter partition data were recorded and statistically analysed using the general linear model statistical procedures. Comparisons among treatment means less than six were made with the Least significant square and up to six and above with the Duncan multiple range test (p = 0.05). Results were compared with the previously reported root rot incidences and severities from the same cultivars. Results showed cultivar TME-1; previously reported to have the highest root rot incidence of 52.6% and a severity of 21.3% at 12 months after planting in Sabongidda-Ora humid forest, to have the lowest dry matter partition of 367.4 g to roots in the same location, 12 months after planting. This was significantly lower than the 804.1 g of TMS 4(2)1425 and the 667.6 g of TMS 30572 recorded in the same location; cultivars TMS 4(2)1425 and TMS 30572 have also been reported to have the lowest root rot incidences of 0 and 6.4% and severities of 0-0.5% at the Ibadan derived savanna. The trend was the same during the second year planting. The results show clearly that root rot can have significantly negative effect on the dry matter partition to the storage roots of root rot susceptible cassava cultivar.