A simple microfluidic thread-based analytical device (mTAD) for determination of phosphorus content in fertilizers based on the formation of phosphomolybdenum blue (PMB) complex was proposed. The proposed mTAD was simply fabricated by stitching the 100 % cotton thread to the polyethylene (PE) mesh canvas. A color developing reagent, which are the mixture of sulfuric acid, ammonium molybdate, potassium antimony tartrate, and ascorbic acid, was firstly loaded into the middle of the thread. A sample solution was subsequently introduced into the same position to form PMB. A digital camera and image processing program were employed for evaluating color intensity of PMB. Variable parameters affecting the mTAD efficiencies were optimized i.e., solution volumes, chemical concentrations, and reaction time.  The applicability of the proposed mTAD method was evaluated by analyzing fertilizer samples. The accuracy as expressed by percentages of recovery ranged between 83 and 96 %. The method was highly reproducible with the relative standard deviation (RSD) of 0.84 % (1 mgP/L), 0.92 % (3 mgP/L) and 1.04 % (10 mgP/L) for 10 replicates. The main features of the system are the used of commonly available materials, simple and rapid fabrication, small scale, reduced chemical waste, less sample consumption, and low-cost. HIGHLIGHTS Simple materials such as 100 % cotton thread and PE mesh canvas can be used for fabricating µTAD The proposed µTAD method was fast analysis and good sensitivity (as low as nmol P level within 6 minutes) by using small amount of reagent and sample solutions The method was successfully determining the phosphorus content in fertilizers GRAPHICAL ABSTRACT