There are many challenges facing the use of alendronate sodium for the treatment of osteoporosis such as low bioavailability of 0.6% and oesophageal ulceration with bleeding. Due to the aforementioned limitation, the main objective of this research is to utilize a statistical experimental design in the formulation and optimization of alendronate in the form of controlled release biodegradable intramuscular in-situ gel. A Box-Behnken experimental design employing Statgraphics® software was used to develop an optimized in-situ gel formulation and to estimate the effects of Poly-DL-lactide-coglycolide as a primary polymer, the copolymer polycaprolactone, and lipid surfactant capryol 90. Every system was evaluated for gellation character, and in vitro release. As a novel technique for evaluation of the in-situ gel, in-vivo biodegradability rate was estimated in rats. Pharmacokinetic parameters were assessed in rabbits. The results indicated a significant effect of the copolymer and lipid surfactant on initial burst, and a significant effect of the primary and copolymer on drug percentage released. The optimum formulation showed a 5% initial burst, an in-vivo biodegradability rate estimated at 8% every seven days in rats, and the pharmacokinetic evaluation revealed that alendronate sodium mean residence time extended to 102 days in rabbits. In conclusion, the optimum biodegradable intramuscular in-situ gel formulations is a promising approach for providing higher bioavailability, extended release for more than three months, with elimination of esophageal side effects.