Monthly yield variation in rubber cultivations is common and it affects the livelihood of rubber smallholders and also the cash flows of plantation companies. The effect is more pronounced in rubber harvesters, workers, and other stakeholders as their income levels are partly governed by the monthly financial performance of the cultivation. This uncertain income levels results in the out migration of work force, causing the declining of rubber harvesters and other workers in WL3, Agro Ecological zone. This has become a major problem faced by the entire plantation industry in Sri Lanka. Thus a thorough knowledge on the variability of yield is essential for accurate estimation of monthly yields and income levels and thereby planning marketing and related activities. Therefore, the main objective of this study was to establish variation pattern in the yield components of two Hevea Brasiliensis clones grown in WL3 agro ecological zone in the country and to find possible reasons for such variation. Further, ways of enhancing yield and income levels were also looked at using the Ellakanda and Katuhenadivisons of Sorana Estate managed by Kotagala Plantation PLC as the study site. Based on the previous literature, relevant theories were formulated; independent and dependent factors that would result in the monthly yield variation and the required information to be collected were identified. Primary data were collected using tapping blocks of the selected divisions along with relevant meteorological data. The raw data were classified to purposeful and usable categories and were tabulated for statistical inferences. Results revealed that the physiological ability of the tree to produce latex, number of tapping days and the rainfall pattern as the main factors which affect the monthly yield variation of RRIC 121 & BPM 24 rubber clones cultivated in WL3 Agro Ecological zone of the country.