Yogurt was prepared from raw milk and oolong tea powder with added L-theanine and muscovado sugar using a starter culture of lactic acid bacteria. The effects of the concentration of oolong tea powder, muscovado sugar and L-theanine and inoculum size on the pH value, acidity, viscosity, water-holding capacity and sensory score of yoghurt were investigated by using a combination of one-factor-at-a-time (OFAT) method and orthogonal array design (OAD). The results showed that under the conditions of 0.3% oolong tea powder concentration, 8% muscovado sugar concentration, 0.09% L-theanine concentration and 0.010% inoculum size, the sensory score, pH value, acidity, water-holding capacity, and total viable count of the prepared yogurt were 96 points, 4.54, 72 °T, 67.34%, and 5.78 × 109 CFU/g, respectively. The product had a rich flavor, bright color, exquisite texture, prominent muscovado sugar-like flavor, strong aroma, and smooth taste without suspended particles.