The Australian Open champion and fourth seed Kerber needed just 65 minutes to book a spot in the quarter-finals at the All England Club, reports Efe.
The 28-year-old German committed just nine unforced errors in the match and was never broken by World No.49 Doi, who failed to convert on two break opportunities.
Doi, a 25-year-old left-hander, committed 25 unforced errors and was broken four times. Kerber, a semi-finalist at Wimbledon in 2012, pushed her career head-to-head record against Doi to 5-0.
The two played in January in Melbourne, with Kerber having to save a match point in her 6-7 (4-7), 7-6 (8-6), 6-3 victory over the Japanese player.
The German went on to win her first Grand Slam title in Melbourne with a 6-4, 3-6, 6-3 victory over American World No.1 Serena Williams in the Australian Open final.
Kerber will play the winner of the match between Romanian fifth seed Simona Halep and American ninth seed Madison Keys.