Aims: The study assessed the effects of different levels of cow manure application on above ground growth characteristics and herbage production of Brachiaria ruziziensis (Congo signal grass) in tropical sub-humid environment on arable land. The rationale behind being contribute to better understanding of how the growth and yield components of B. ruziziensis respond to varied levels of cow manure application Study Design: Complete Randomized Block Design (CRBD). Place and Duration of Study: Field experiment was conducted at Magadu Dairy Farm, located in Morogoro, Tanzania, from February to June, 2014. Methodology: Three (3) blocks (replications), 4 treatments (0, 5, 10 and 15 t/ha cow manurelevels), 3 m inter-block distance, 12 plots and 0.5 m inter-plot distance. Pre-plant spread of manure into plots at varying levels followed by planting of B. ruziziensis stem cuttings. Repetitive measurement of several above ground growth parameters at 2 weeks interval post planting up to the 10th week. At the end, the pasture stand was harvested and the above ground dry matter (DM) yield was estimated. One way ANOVA under SAS computer program was used to test if there was significant difference among the treatments at P =.05. Results: Cow manure application had a significant effect on stem height, tiller and leaf number perplant (P < .0001), in which each subsequent increase in manure application was increasing growth of these parameters. Moreover, the DM yield differed significantly across all treatments (P < .001). However, there was no significant difference in DM yield between 10 and 15 t/ha manure application rates (P = .76). Conclusion: Cow manure was found to improve productivity of B. ruziziensis by increasing stem growth, tiller and leaf numbers, thus DM. Moreover, cow manure application rate of 10 t/ha was found to be ideal level for maximum DM yield (13.5 t/ha) under the conditions of this study.