Filler and fiber material loading and surface modification are some of the factors that significantly influences the tensile properties of the natural fiber-reinforced plastic composites. It is therefore pertinent that they are suitably selected in order to yield the optimum tensile properties. In this work, Box-Behnken Design was selected as experimental design approach. Fiber-reinforced PLA composites were prepared using compression molding. Rice husks and clay were utilized as fiber and filler materials respectively. The factors, namely clay filler loading (1-5 wt.%), rice husk fiber loading (10-30 wt.%), alkali concentration (0-4 wt.%), rice husk variety (K85, K98) and alkali type (NaOH, Mg(OH)₂) were varied with a total of 68 individual experiments. ANOVA was used to determine the significance of the factors affecting composites’ tensile strength. Results from ANOVA also revealed that the reduced cubic model best fits the tensile strength response. Derringer’s desirability function revealed that the variable values leading to optimum tensile strength (33.67 MPa) were 4.99 wt.%, 12.17 wt.% and 3.97 wt.% for filler loading, fiber loading and alkali concentration, respectively.