In the present work, we discuss how oxidation conditions can affect the physical properties of oxidized alginate and crosslinking it with gelatin. We show that the amount of aldehyde groups produced on oxidized alginate backbone increases by increasing alginate concentration even in constant molar ratio of sodium periodate to alginate's repeating units. Increasing the concentration of alginate solution, promote the extent of chain scission and decreases the molecular weight of oxidized alginate, which can be due to the increased possibility of molecular collisions and oxidizing two adjacent uronic acids in the chain. By changing the oxidation condition, therefore, we can produce oxidized alginate with same degree of oxidation but different molecular weights, which change the sol-gel state of alginate-gelatin mixtures. Using oxidized alginates with different molecular weights, we suggest that the aldehyde end groups in alginate chains have the dominant effect in crosslinking with gelatin.