In this work, sensors were prepared by depositing the pH sensitive indicator (bromothymol blue) entrapped in polyaniline sol-gel onto the un-cladded middle potion of optical fiber. Polyaniline is sensitive to pH. However, it is important to study ways to increase sensitivity of the indicator by improving a combination of the materials used and pH sensor fabrication method. The fabrication and characterisation of optical fiber pH sensor on absorption intensity in arbitrary unit (a.u) were evaluated and optimised. The better sensitivity of the optical pH sensor was used to identify the optimum setting for number of layers deposited, coated length, and withdrawal rate. Thickness of the membrane film depends on the number of deposited layers and withdrawal speed which mainly affects sensitivity. The sensitivity of the optical pH sensor represents the slope (a.u/pH) of the absorbance intensities in pH 4, 5, 7, 9 and 10. Results obtained herein suggest that the optimised setting for bromothymol blue sol-gel coated optical fiber with thickness of 285.4 nm is 4 deposited layers, 20mm/s withdrawal rate and 0.5 cm coated length.