Reaction time (RT) is important in learning. Relationship of RT to Intelligent Quotient (IQ) and Working Memory (WM) has not been studied in Sri Lankans. To measure the visual RT(VRT), discrimination RT (DRT) and choice RT (CRT) of young adults and to correlate these reaction times (RTs) to IQ and WM. A cross sectional study was conducted among 200 volunteers (18-28 years). RTs were measured using the "reaction timer software" developed locally. WM was assessed using "digit span backward test (DSBT)". IQ was assessed using Raven's standard progressive matrices (RSPM). Mean, SD of VRT, CRT and DRT in males were 292.85±32.88ms, 395.75±75.62ms and 407.45±82.11ms respectively. The respective values in females were 317.85±43.15ms, 452.68±96.47ms and 454.26±93.5ms. RTs were faster (p<0.05) in males. VRT was faster (p<0.05) than CRT and DRT in both sexes. CRT and DRT did not differ significantly in both sexes (p>0.05). Mean IQ scores of males and females were 52.17± 6.2 and 51.74±6.2. Respective DSBT scores were 7.55±1.62 and 7.64±1.33. IQ and DSBT scores were not differed (p>0.05) between sexes. RTs had negative correlations with IQ and DSBT score. Only the correlations of IQ with VRT of males (-0.203) and DRT (-0.225) and CRT (-0.235) of females were significant (p<0.05). Significant negative correlation (-0.293) of DSBT score was observed with DRT of females only. RTs were shorter in males. IQ and WM capacity showed negative correlations with RTs. Further studies are necessary to assess the contribution of the processing speed on the IQ and WMC.