To provide thick green tea extract liquid having low production costs, enabling effective utilization of resources, and excellent in taste, flavor and color each inherent in tea; to provide a method for producing the thick green tea extract liquid; and to provide a diluted beverage comprising the thick green tea extract liquid.

The thick green tea extract liquid is obtained by decocting tea leaves with water so as to have a tannin concentration of 120-200 mg%. At least 3.0 wt.% of galacto-oligosaccharide having a concentration 12.5 times or more the tannin concentration is added before the temperature of the thick green tea extract liquid becomes ≤10°C so as to cause no turbidity and to make an eater feel no sweetness even when decreasing down to 5°C.