Lidar is a very good tool for lower and middle atmospheric explorations. A Nd:YAG laser based Rayleigh Lidar was set up, at a high altitude observatory, Mt. Abu (24.5^o N, 72.7^o E, MSL height 1.7 km), in the Indian sub-tropical region. Temperature climatology and long term trends in the middle atmosphere has been studied using about 19 years (November 1997 to May 2016, with some data gaps) lidar observations. A multivariable analysis is used to consider natural variability (Solar Cycle and QBO) and similarly the changes in stratospheric ozone concentration due to anthropogenic activity have also been taken into account in trends estimations. We have selected different height regions 30-40, 40-50 and 50-60 km for trends analysis. Linear Regression analysis is applied to calculate temperature trend in different altitude regions. Considering the signature of seasonal, QBO and solar cycle variability, a linear decreasing temperature (cooling) has been found. Observed temperature trend is the strongest (-0.38 ± 0.15 K/year) at stratopause level (45 km) and the weakest (-0.14 ± 0.28 K/year) at 55 km during April. Seasonally, stronger temperature trends are found during winter -5.4 ± 2.8, -5.1 ± 2.1 and -2.1 ± 1.9 K/decade at 35, 45 and 55 km, respectively. The temperature trends during summer months are -2.2 ± 1.8, -2.8 ± 1.4 and -2.5 ± 1.6 K/decade at 35, 45 and 55 km, respectively. Lidar observed temperature trends over Mt. Abu are also compared with HALOE (onboard UARS) and SABER (onboard TIMED) temperature observations.