The best time to visit Kenya is during the Dry season from late June to October (these are the best wildlife viewing months). The wildebeest migration usually reaches the Masai Mara in August and remains until October when they move back to the Serengeti in Tanzania. Wildlife viewing is good year-round, but this can differ for some parks. See below to learn when to visit which park.
June to October –Dry Season
Wildlife Photos

November to May –Wet Season
Wildlife Photos
Best Time To Go by Major Park
The Masai Mara National Reserve offers great wildlife viewing throughout the year. In the peak of the rainy season, most other parks, especially in the highlands and along the coast, can be problematic with regards to heat, humidity and continuous rain. Some of the lodges close as a result. The dry months offer quality wildlife viewing throughout Kenya.