This is an investigative study on how effective are the existing assembly instructions and new design instructions in terms of usability. The effective assembly instructions assist novice users to assemble the products at home. The portable toilet cardboard is used as a case study with four types of instructions. Four groups composed of twenty-four subjects are assigned to assemble the cardboard with usability testing method. The result shows that the step-by-step procedure with the guiding part on the product is the most effective in terms of time to complete each task and number of errors.

Keywords: Usability, Instruction, Assembly, Portable toilet.