Growth and development of four dominant species of Trentepohlia was analysed by inoculating each species of Trentepohlia on a solidified BBM (Modified) with 2 % agar and keeping under different relative humidity (33%, 55%, 75%, 85% and 98%). It was clearly observed that growth of all Trentepohlia species were optimum at 98 % relative humidity. With increase in relative humidity the length and width of the filament cells, apical cells and sporangia increased with incubation period from first to fifth weeks. At 98 % RH growth and survival of all four species studied was high, whereas at lower relative humidity retarded growth could be observed. Comparatively, T. diffracta and T. abietina showed better growth in different relative humidity. Significant increase in cells width and sporangia width was observed after three weeks of inoculation and in the 5th week growth of new filaments could be observed.