Canola is the principal cash crop in the Prairie Provinces of Canada and majority of it is grown in the Parkland zone where many soils are deficient or potentially deficient in plant-available sulphur (S) for canola, because it has high requirements for S. Because S is immobile in plants, its deficiency at any growth stage during growing can drastically reduce canola yield. On soils that are marginally low in plant-available S at seeding but well fertilized with N and P, sulphur deficiencies can manifest themselves during peak vegetative growing periods of canola, or later at flowering and seed formation. Field experiments were conducted in 1998 and 1999 in northeastern Saskatchewan to find if seed yield of canola on S-deficient soils can be restored to its normal level by applying S fertilizer at different growth stages. Potassium sulphate was applied at 15 and 30 kg S/ha rates at sowing, bolting and flowering stages of canola. Methods of S application were incorporation into soil, sideband and in seedrow at sowing, and topdress and foliar application at bolting and flowering. In all experiments, there was a marked seed yield increase response to N + S fertilization, no response to S alone and negative response to N alone. In one experiment, increases in canola yield from S fertilizer were generally similar for various times and methods of S application. But in other three experiments, topdressing increased seed yield less than foliar applied S at bolting and flowering. Yield increase was lower when S fertilizer was applied at flowering compared to that obtained at bolting or sowing. Applications of S fertilizer at sowing gave the greatest increase and topdress applications at flowering gave the lowest increase in seed yield. Application of S fertilizer also increased oil and protein content in canola seed. The results suggest that for canola S deficiency can be corrected and seed yields restored with application of sulphate-S fertilizer in the growing season, substantially until bolting stage and moderately as late as early flowering stage. The findings also indicated that there is a need of adequate rainfall after topdress application to move the S fertilizer into the subsoil where roots can intercept it. Foliar application of S was more effective than topdressing in restoring seed yield in S-deficient canola if the S fertilizer had to be applied in the growing season.