A study was conducted to determine the interaction of roughage quality and urea-ammonization on the luminal degradation properties of low quality roughage diets. Four rumen fistulae Jersey cows were fed on a basal diet of either urea-treated or untreated Eragrostis uvula hay. These basal diets were supplemented with concentrate composed of maize meal (78%) and cotton seed cake (22%). The concentrates contributed 0, 25, 50 and 75% of the total ration and hay the rest. The experiment consisted of 6 periods. Each period lasted 19 days, comprising 12 days of adaptation to the experimental diet followed by 6 days degradability measurements and 1-day collection of rumen fluid. During each period the 4 cows were randomly allocated to 4 of the 8 dietary treatments, ensuring that each diet was fed to 3 animals during the entire experimental period. The pH of the rumen fluid ranged between 6.5 and 6.8 for all diets. Rumen ammonia (NH3) concentration was higher (P<0.002) when the basal diet consisted of urea-treated hay. Increasing the concentrate proportion in the diet had the desired effect of increasing rumen NH3 concentration without severely affecting the pH. Urea-ammonization increased (P<0.0001) the slowly degradable fraction (B), potential degradability (PD), effective degradability (ED) of dry matter (DM), decreased (P>0.05) lag time (LT) but had no effect on the rate of degradation (c) of DM. Maximum and minimum degradability values of the B-fraction, PD and ED of DM were obtained at the 25 and 75% concentrate levels, respectively for both urea-treated and untreated diets. Within urea-ammonization, roughage type increased (P<0.001) the B-fraction, PD and ED of DM. Ryegrass degraded almost three to four times faster than urea-treated oat or untreated wheat straw. Urea-ammonization was less effective in increasing DM degradation rate of ryegrass compared to wheat straw. Results show that low quality roughages such as wheat straw benefited relatively the most from urea-