The variability of ionospheric slab thickness at high latitudes during the high solar activity period 2005, we have selected a high latitude station Casey (66.3 S, 110.6 E) in the southern polar region. The results show that the diurnal variability of slab thickness shows that the night time values are higher than the day time values. A significant difference is observed between the day time and night time values during equinoxial months. The diurnal variability at Casey during the high solar activity period is also characterized by a pre sunrise peak in some months which does not occur around the same time as well as is not pronounced during the other months of year. The monthly variability of slab thickness at high latitude follows the semi-annual type of variability with two peaks during the month of March and September. The value of slab thickness is highest during the equinox while least in the summer season. We also notice that the night time values of slab thickness are higher than the day time during all the seasons. The pre sunrise peak is much pronounced during the summer and equinox seasons. The monthly variability of slab thickness follows a very good association with X-ray flux (1-8Å) and EUV flux (26-34nm) and very weak association with the F10.7cm. The correlation coefficients of slab thickness with F 10.7 cm, X-ray Flux (1-8Å) and EUV Flux (26-34nm) are 0.28, 0.58 and 0.60 respectively.