Pope Francis said on Wednesday he wanted to offer "spiritual and material" support on his first tour of Africa, where he will address a fast-growing Catholic congregation and seek to heal divisions between Christians and Muslims.
Millions of Christians - Catholics and others - are expected to turn out for public celebrations of Mass, presenting a challenge for national security forces to keep the pontiff and the huge crowds safe.
About 30 percent of Kenya's 45 million people are baptized Catholics, including President Uhuru Kenyatta.
He will address the faithful in a public Mass at Nairobi University on Thursday - declared a national holiday - and is expected to seek to heal ethnic rifts that have long plagued Kenya.