ABSTRACT This paper proposes the design of an approximated fractional-order low-pass Bessel filter using various optimisation techniques. Simulated annealing (SA), nonlinear least square (NLS), and firefly (FF) optimisation methods are applied for the designing of (1 + α) order low-pass Bessel filter. Stability analysis has been attempted for the proposed fractional-order Bessel filter in W-plane for α ranging from 0.1 to 0.9 in the interval of 0.1. The best optimisation technique in terms of error in gain, cut-off frequency, and stopband attenuation is validated on Biquad. Further, KHN Biquad has been simulated using SPICE to validate 1.2, 1.5, and 1.8 order Bessel filters. MATLAB and SPICE simulated results of gain, cut-off frequency, and stopband attenuation have been compared for the proposed Bessel filter. MATLAB simulated magnitude response shows a great extent of closeness with SPICE simulated magnitude response. Monte Carlo analysis has also been done in the SPICE environment.