De Ocampo started playing organized basketball at the Saint Francis of Assisi College System Doves together with his brother, Yancy. The De Ocampo brothers led the varsity squad to several NCRAA titles. Upon the exit of the older De Ocampo, the Doves became Ranidel's team. Thus, he led the squad into several statistical categories such as in scoring and rebounding. He won four NCRAA MVP plums along with the legacy as arguably the finest player in the history of the NCRAA.
In 2004, after a celebrated collegiate career at St. Francis, De Ocampo decided to turn pro and enter the PBA draft. He was selected by the FedEx Express as the fourth overall pick, having selected ahead of higher profile players such as classy UE point guard Paul Artadi, multi-titled PBL veteran Gary David and former King Eagle Wesley Gonzales.
During his rookie year, he played alongside his brother Yancy. Thus, he played in a total of 59 games and averaged decent rookie numbers of 7.46 points and 4.58 rebounds while playing a little over 21 minutes of action per game.
After a so-so performance in his first year, he made an impact in the 2005-06 season by improving his rookie numbers 7.5 points per game to 13.3 in his sophomore year in 37 of 51 games played. He also registered 6.7 rebounds and 2.4 assists in that year.