Simultaneous measurement of gross alpha and gross beta activities by liquid scintillation counting technique using LKB Wallac Quantulus 1220 liquid scintillation counter (LSC) equipped with Pulse Shape Analyzer (PSA) is described. Three sets of pure alpha and pure beta standards simulating the activity concentration values of real samples in terms of a/b activity ratios were used to calibrate the LSC. Calibration methodology for the Quantulus 1220 with respect to the above measurements using ²⁴¹Am and ⁹⁰Sr/⁹⁰Y  standards of respective activity concentrations of  ~25 dpm and ~10⁴ dpm is described in detail. Also highlighted the need to calibrate the LSC using another set of ²⁴¹Am and ⁹⁰Sr/⁹⁰Y standards of low and high activity concentrations respectively. The practicability and working performance of these calibration plots was checked by the validation trials with test samples spiked with ²⁴¹Am and ⁹⁰Sr/⁹⁰Y covering range of a/b activity ratios from 1:1 to 1:50.