Abstract: Three crossbred Holstein-Friesian dairy cows in mid-late lactation were randomly allocated to three ratio of cassava hay (CH) and soybean meal (SBM) (CH:SBM) in concentrate supplement treatments(0:100, 60:40, 100:0) according to a 3 x 3 Latin square design. Concentrate mixture containing 16 %CP was given to animals at two equal parts (2 % of body weight per day) while urea-treated rice straw (5 %urea) (UTRS) was given on ad libitum. The experiment revealed that increasing CH:SBM ratio in concentrate had no effect on dry matter intake and digestibility while reduced concentrations of ruminal ammonia nitrogen (NH3-N) and blood urea nitrogen (BUN) were reduced. Milk yield across treatments were similar (8.0-8.5 kg/hd/d) while fat contents of milk tended to linearly increase as ratio of CH to SBM in concentrate increased. Moreover, increasing levels of CH to SBM ratio in concentrate linearly increased income over feed thus resulted in more milk income return. Conclusions can be made that CH should be recommended used as a protein source replacement a soybean meal in concentrate for a sustainable dairy production in the tropics.