The empirical formula are established to predict the size and fusion penetration of deep fillet welds on the assumption that a cross sectional form of fillet weld is a semi-ellipse. The data of experimental results are obtained from positioned one pass welding of mild steel Tee-joints with automatic submerged arc welding. The size of a fillet weld, that is throat thickness or leg length, is determined as a function of welding current, welding speed, and deposition rate of filler metal. Where, the deposition rate is expressed as a function of electrode diameter, extention of electrode, arc voltage, welding current, and a material constant defined as the coefficient of deposition rate. The depth of fusion penetration is determined as a function of leg length and theoretical fusion penetration. Where, the theoretical penetration is derived from the moving point heat source theory and expressed as a function of the deposition rate, welding current, welding speed, and a material constant defined as the coefficient of fusion penetration. Appropriate quantitative correlation of the welding parameters stated above are investigated experimentally in order to hold sound profiles of fillet welds, and the empirical formulae to control proper welding condition are also established. The utility of all empirical formulae are confirmed by practical welding tests.