Mr Odinga claims the vote was rigged in favour of President Kenyatta.
Kenya's opposition leader Raila Odinga says he will mount a legal challenge to the result of last week's presidential election, which he claims was rigged.
Mr Odinga, who was defeated by incumbent Uhuru Kenyatta, had previously rejected an appeal against the outcome.
Foreign observers had described the election as free and fair.
The international community has urged calm amid fears that the fraud claims could result in violence.
Mr Odinga said the opposition had collected concrete evidence of massive irregularities that were allegedly used to rig the vote.
The official results gave President Kenyatta about 54% of the vote, and Mr Odinga 45%.
"We have now decided to move to the Supreme Court to lay before the world the making of a computer-generated leadership," he told journalists.(BBC)