Cell suspension cultures of Orthosiphon stamineus were established from friable calluses produced from leaf pieces of in vitro plantlets that were derived from nodal segments of the mother plants collected from three different geographical locations. Eight lines were eventually selected after seven subculture cycles based on the growth characteristic (plant height) of the plantlets from the three locations: two fast-growing lines (>5.1 cm tall), three intermediate-growing lines (3.1–5.0 cm tall), and three slow-growing lines (<3.0 cm tall). All eight lines grew well in liquid Murashige and Skoog medium supplemented with 4.5 μM 2,4-dichlorophenoxyacetic acid (2, 4-D) and 5.4 μM 1-naphthaleneacetic acid (NAA). All cell lines exhibited the same growth pattern but produced different maximum cell biomass when cultured in this medium. The time of harvesting the plant cells from the culture medium and the geographical source of the original plant material were both found to affect the production of rosmarinic acid (RA) in cell cultures. Two cell lines were successfully selected and identified to produce high amounts of RA. These cell lines were a fast-growing cell line from Air Itam, Penang and an intermediate-growing cell line from Relau Agriculture Research Centre, Penang which could produce 5% [(w/w) dry weight] and 4.5% [(w/w) dry weight] of RA, respectively.