Alternaria blight incurring loss both at pre and post-harvest stages in tomato caused by Alternaria alternata become an important constraint for tomato producers in Rajasthan. The severity of this disease generating significant economic losses in crops has been increasing daily for the last few years in Rajasthan due to environmental changes. Field experiments were carried out to examine the development of Alternaria blight in tomato relevant to weather conditions during zaid 2017 and 2018 at SKNAU Jobner (Jaipur). Results showed that maximum temperature (r= 0.9032 Unit in 2017 and 0.8893 in 2018), minimum temperature (r=-0.8590 in 2017 and 0.8512 in 2018), relative humidity maximum (r=-0.6184 in 2017 and -0.8562 in 2017), relative humidity minimum (r=- 0.6840 in 2017 and -0.5477 in 2018) and rainfall (r=-0.6161 in 2017) had shown significant negative correlation with disease severity index (DSI). The mean value of the minimum and maximum temperature during this period ranged from 15.630C to 35.740C and 15.750C to 36.240C during 2017 and 2018, respectively. Development of disease observed in favourable mean relative humidity ranging from 25.33 to 63.00 and 16.66 to 58.00 per cent. The coefficient of multiple determinations (R2) was 74.50 and 92.40 per cent during 2017 and 2018, respectively.